NOTES ON NEW ENGLAND ALGAE

ROY. M. WHELDEN

Casual observation of collections of freshwater algae from the numerous waters of Maine reveals an algal flora of surprising richness; more careful attention shows it to be well worth intensive study to which the following notes may be considered only as an introduction.

The collections on which these notes are based have been selected from several hundreds of vials of algal material gathered in every month of the year through seventeen years. Beyond the statement that no collection noted here was made from any large body of water, either lake or river, no description can be made to include the many habitats from which collections were made. One might stress the fact that several separate collections were made from what appeared to be the least promising places, such as a shallow rain pool formed in a foot-path.Despite what seemed to be a sterile habitat, a sample nevertheless was taken and later found to contain an abundance of Closterium macilentum, a large percentage of which was in some stage of conjugation. This and other habitats to be mentioned subsequently seem to justify the statement that no place should be passed by too carelessly, since surprising discoveries may be completely missed by such lack of attention.

As originally planned, collections were made as frequently as feasible from as wide a variety of habitats as possible : from densely shaded brooks or pools; from cold water and some from shallow pools in full sunlight when the water at the time of collecting was extremely warm; from crystal clear waters to some of deepest brown color. Final selection of material to be considered is due in part to its rarity, to the occurrence of anomalous forms, to noteworthy variability, and to stages of reproduction.

MYXOPHYCEAE

The presence of blue-green algae was frequently noted in a large majority of the collection; in no case did these algae occur in any quantity. One of the most interesting of these was Eucapsis alpine Clements and Shantz (Fig. 1) which was found in abundance in a single station, a vegetation-filled pool in which the water was only a few inches deep, with several feet of slimy brown ooze beneath. The Eucapsis colonies varied in size from small ones having only sixteen cells to large compound groups of more than five hundred cells. The first specimens observed were collected in early June; later they were found in abundance up to mid-November. Many colonies were examined and the component cells carefully measured. When mature the cells were of strikingly uniform diameter. Different colonies showed a rather wide range of cell size : many were formed of cells 2-3 µ in diameter – var. minor Skuja ; others, found with the small ones, were 3-4 µ in diameter. Very many more had cells 6-6.5 µ in diameter; often the large-celled colonies were composed of the largest number of cells. The presence of this alga was observed at this station from 1927 to 1940. Not once, despite repeated search, was it found in any other of the extremely numerous habitats, some very like this one and only a few rods away. Frogs and a variety of wading and swimming birds are frequent here; yet it would seem that they have never successfully transported this alga elsewhere.

Occurring in the same marsh with Eucapsis, and in many other places throughout the southern half of the state is Glaucocystis nostochinearum Itzigs. This alga seems always to occur sparingly.

In one shallow marsh, specimens of Anabaena were found in small numbers, always occurring singly and devoid of any obvious sheath. The spherical cells comprising each filament were 1.5 µ in diameter or slightly less; the heterocysts were also spherical and 2-2.5 µ in diameter; akinetes were always remote from the heterocysts and were cylindrical, 4.5 µ in diameter and 18.5-22 µ long. While somewhat smaller in all dimensions, this seems to be Anabaena minutissima Lemm. The only specimens found were from this single station Anabaena flos-aquae (Lyngb.) Bréb. Is found rather frequently throughout this region. Its var. minor W. West was found in one place in large amounts. The numerous filaments were of cells 2.7 x 2.0 µ in diameter. The heterocysts were 2.8-4 µ diameter, and the akinetes, present in large numbers, varied from 5.9x12 µ to 8.4x 22 µ.

The many other species of blue-green algae found in this region may never have been reported as occurring there. However they are of such common occurrence there and elsewhere that their presence may be expected. For the present at least they remain unnoted.

CHLOROPHYCEAE

            Among the green algae one finds many of particular interest. One of these was a species of Closteridium (Fig.7) which occurred rather abundantly in a small marsh pool. The majority of the solitary cells were smi-circular in shape with one side straight or only slightly curved. Each pole bears a single pointed spine which may be straight but frequently is distinctly curved. The cell wall is thin. The single chloroplastid fills nearly the entire cell and contains a single pyrenoid and also a single nucleus, the latter approximately centrally located in the cell. These cells vary considerably in size, being usually between 75 and 95 µ long (including spines) and 30-40 µ in maximum diameter. The spines are 11-13 µ long. The smallest cell measured was only 63 µ long and 23.5 µ in diameter. Among the many cells seen were large number apparently in various stages of divison. The most noticeable feature of these was the presence of two distinct pyrenoids, which probably resulted from the division of the single pyrenoid normally present. Once divided the two pyrenoids seem to move apart subsequent to which there appears a distinct division of the chloroplastid, leaving a single cell with two distinct plastids. Several of these were seen. Further stages showing that actual cell division did occur were not found. Cells in which these stages occurred were 100 – 105 µ long but with diameters of the same magnitude as had the normal cell. Despite the rather larger dimensions and coarser habit this alga seems to agree quite well with descriptions of C. siamensi (W. and G. S. West) Wille, reported in this country by Prescott.

            Occurring with the Eucapsis considered above and apparently also restricted to the one pool, is a species of Tetraëdron  which has appeared regularly in collections made throughout many years. The thick-walled cells are triangular with sides generally strongly convex, or occasionally straight or slightly concave. Each angle bears a single stout, curved, straight or rarely slightly hooked spine. The single choloroplastid contains no pyrenoid. The length of the cell, spines included, varied from 102-118 µ, without spines from 77-84 µ ; the breadth, without spines, from 50-62 µ. The length of the spines is 11.3-17 µ.

            W. and G. S. West in 1895 described, without any figure, as Tetraëdron tortum, a species which has much in common with that considered here. Their species was relatively narrower, 44 µ being given as maximum breadth, twisted, and with sharp spines about 30 µ long. The specimens herein described are much plumper, in end view generally presenting sub-circular outline; they rarely, if ever, show a shape that could be described as twisted, and they have much shorter spines. This combination of characters seems sufficient to justify describing this as a new species,

Tetraëdron mainensis n. sp. (Fig. 4) .

Tetraëdron   cellulis magnis, tumidis, trigonis, lateribus convexis, vel rectis vel rarissisme plus minus concavis; anguli spinas crassas rectas, vel arcuatas vel plus minusque unicanatas ferunt; membrane crassa glabara; cellulae cum spinis 102-118 µ longitudine et sine spinis 77-84 µ longitudine, 50-62 µ latitudine, 40-51 µ crassitudine; spinae 11.3-17 µ.

          The desmids have always received much attention, partly because of the striking variety of their many species and their beautifully symmetrical shapes. No less interesting are the many problem the offer – problems of distribution, of habitat, of variability, of reproduction have frequently drawn attention. In the region considered in this paper, desmids are one of the most abundantly ecountered groups of algae, and certainly are not devoid of interest.

            One of the commonest species, occurring throughout the region, is the ubiquitous Nerium digitus (Ehrenb.) Itzigs. And Rothe. Attention was drawn to the numerous observed specimens by the wide range in size: the smallest specimens were 80-85 µ long and about 30 µ broad, and a well graduated series existed which varied from these smallest specimens up to those that are 300 µ and more long and 90-100 µ board. The cell outlines varied from sub-cylindrical to fusiform, with broadly rounded to truncate ends.

            Closterium occur in abundance throughout the region. Collections may frequently be made in which a single species occurs, but more frequently specimens of this genus are found scattered among other algae. Zygospores are not infrequently found, developing at all seasons of the year. One pool gave Cl.  rostratum Ehrenb. Zygospores in April; in July, zygospores of Cl. Setaceum Ehrenb. Was conjugating, but occasionally one finds instance in which large numbers are seemingly forced to conjugate at the same time. The Closterium macilentum Breb. Mentioned earlier offers such a case. In this collection many of the zygospores departed considerably from the spherical shape described by Brebisson for this species, and were much larger. The example in Fig. 3 is 53 x 57 µ and rather vaguely angular in shape. The cells contributing to this were 420 x 17 µ and 460 x 15 µ. The zygospores of Cl. Ralfsii var. hybridum Rabenh. Were spherical and 70 -80 µ in diameter.

Many interesting problems other than zygospore formation present themselves here. Sigmoid forms occur very frequently ; examination shows that in some cases the cells which appear as sigmoid are really of spiral form. In like manner the striae or ribs so characteristic of many species may depart from margin and run in spirals around the cell. More frequently the spiralling is restricted to the apical portion of each semi-cell. Another feature in the cells of this genus is the gypsum particles found in the terminal vacuoles. Variation of these granules is often great, as in a collection of Closterium angustatum Kutz., in which some cells had vacuoles containing as many as sixteen long slender granules, and many but a single large nearly spherical one. The granules in the two ends of a single cell might be quite different. Cells form this same collection showed many with spiral ribs. Some are shown in Fig.5 many other species have a simiar range of variation in granules. Abnormally shaped cells are not infrequently found in collections of this genus. Aready mentioned are the sigoid and spiral  form. Occasionally more abnormal forms appear. The two examples of Closterium striolatum Ehrenb. Shown in Fig. 8 are from a collection in which many such cells occurred. In some the apical portion was almost at a right angle to the cell axis; all degrees of bent cells were found between these and quite a normal cells. No cells was found in which  both ends were abnormal. In a few cases cells were found in the later stages of division, with younger semi-cells of the two daughter cells showing the same type of bending.

            Specimens of Spinoclosterium curvatum Bernard (Fig. 6) have appeared in several widely separated parts of Maine. The cells vary somewhat, especially in the degree curvature and the shape and orientation of the apical spines. The latter are usually straight and from 17-21 µ long, but occasionally curved spines are found. Many specimens showed terminal vacuoles containing 8-10 small granules. Cells were frequently found containing specimens of a parasitic fungus (Opidium sp. ? ) so frequently found in Closterium and other desmids.

            Occasionally one finds a collection of desmids which is practically pure, containing  but a single species, in the most unexpected places. One such was gathered from a shallow sand pit into which a small turf of Polytrichum moss had slid. No algae were apparent in the clear water some ten inches deep, yet examination showed the mosses covered with masses of Euastrum oblongum (Grev.) Ralfs. Most of the cells were very uniform in appearance, 155-175 µ long and 82-90 µ broad. One specimen merits notice, and is shown in Fig. 2 (right). First observation indicated that a zygospore was present; examination showed it to be a cell in which division had gone to the formation of a large somewhat spherical mass 108 µ in diameter with a coarsely irregular surface and dense contents of which the nature could not be determined. The specimen shown in Fig. 2 (left) presents certain troublesome points: it is 161 µ long and 80 µ broad; in one semi-cell the upper lateral lobes are rounded, suggesting E. humerosum Ralfs; in the order the corresponding lobes are subquadrate with retuse margins and are characteristic of E.oblongum.

            Anomalous cells result from arrested divisions in the other desmids as well as Eastrum. Fig. 10 shows two such cells of Cosmarium bioculatum Breb., together with a normal cell. In both abnormal cells shown and in several other similar ones seen, specimens of a parasitic fungus occurred.

            Cosmarium subturgidum (Turn.) Scmidle is a rare species described from India. A smaller forma of minor has been found in Asia, Africa and Australia. It is interesting to note that a form should appear in Maine, where it occurred in considerable numbers in a small pool in a Sphagnum bog near the coast. The cells were large, from 2.6-3.7 time as long as broad, distinctly constricted, sinus obtuse, angled; semi-cells ovate with truncately rounded ends; cell-wall smooth expect in apical portion where many coarse irregularly distributed pores appear. Vertical view circular. The chloroplastids are parietal longitudinal bands, 7-8 per semi-cell, and of these 3-4 are visible in face view. The cells are 130-145 µ long, and 46-48 µ in maximum diameter. The isthmus is 38-44 µ broad. These cells are distinct from the species and form by their narrower shape and by the presence of pores at the apex, and so are described as a new form of this apparently rare species (Fig. 9.)

            Species of Micrasterias are among the commonest of the desmids of this region, twenty-four species having been found, mostly in abundance and widely distributed. All species show considerable variation in the nature of the lateral lobbing. Anomalous forms seem however to be relatively rare. Two such cells of Micrasterias rotate (Grev.) Ralfs are shown in Fig. 15. The occurred in a shallow slow-flowing brook of clear cold water in which there were thousands of cells of this species. The few anomalous forms were all of the same nature, represented by individuals in which one semi-cells had the lobes much distorted and sometimes nearly at right angles to the main axis of the cell. No evidence of any disturbing factor could be discovered. Another collection of Micrasterias proved to be of more than passing interest. It was made from a small pool in a brook flowing very slowly through a swamp. Few indeed were the cells found on examination of the material—a few specimens of Closterium, one or two specimens of Staurastrum mucticum Breb., and somewhat larger number of Micrasterias pinnatifida (Kutz.) Ralfs; in others a semi-cell suggested M. oscitans Ralfs. By far the greater number of the semi-cells were not easily assigned to any species. Variations were particularly noticeable in the lateral lobes, which appeared now board , now narrow, nearly entire or provided with prominent apical spines. The variations of the polar lobe were less frequent and often less pronounced, and included an apical margin which varied from straight to strongly convex, and with ends merely angular, or with one tooth or two. Separating the lateral and apical lobes the incision varied from extremely narrow to very broad. In many cases the two sides of a semi-cell varied somewhat, though usually they were of the same general pattern. No noticeable variations could be observed in the other species of desmids present. Four specimens of this Micrasterias pinnatifida (Kutz) Ralfs are shown in Fig. 16  the cells are 58-69 µ long, 63-71 µ broad, and the isthmus is 8-12 µ broad.

            Four species of Xanhidium are here found widely scattered and in abundance. These are X. armatum (Breb.) Rabenh., X. antilopaeum (Breb.) Kutz., X. cristatum (Breb.) Kutz., and X. tetracentrotum Wolle. Other species such as X. subhastiferum W.West and X. pseudobengalicum Gronb., also occur, but infrequently. The commoner species hold particular interest because of the extreme variability which seems to be exhibited. The specimens of X. tetracentrotum shown in Fig. 14 serve to illustrate this very well. All these are from gathering in early August from a small pound. At the time of collecting, the plants were actively dividing, filaments if 4-8 cells being found in abundance. All cells were of normal size for the species, being 38-45 µ long, 35-45 µ broad without spines, and 52-65 µ with them, and 24-26 µ thick. The isthmus was 10-12.5 µ broad. The cells bore a yellowish brown thickened area in the middle of the lateral face; the scrobiculations thereon sometimes formed a semicircle or cresent, but more frequently a complete circle. Within the circle a few accessory scrobiculations often appeared. Greatest irregularity attached to the spines, both in their disposition. The smallest number found was in those cells in which each lateral angle bore a single spine. Other cells bore a pair of spines in each angle, or eight spines for the entire cell. All variations between these were found, the paired spines being in a horizontal plane. One of these is shown in vertical view in Fig. 14, the semi-cell has unpaired spines. In many specimens there were two spines to each angle, but they were in a vertical plane. Often unpaired spines were found above these, the cell shape then becoming subhexagonal instead of elliptical. Many cases were observed in which a prominent papilla appeared instead of a spine. Some specimens presented a decidedly asymmetrical appearance as a result of the very irregular disposition of the spines. All the variations or irregularities noted were cells which could be considered mature, the central ornament being deeply colored or the cell actively dividing.

            Xanthidium antilopaeum (Bréb.) Kutz., is much more widely distributed in this region than is X. tetracentrotum Wolle, several distinct varieties being found. One of these is Irénée’s var. quebecense. Many specimens of the latter are much larger than his, the largest measured being 100 µ long (with spines), 92 µ (without spines), 106 µ wide (with spines), 90 µ (without spines), and the isthmus 16-23 µ broad. The central scrobiculations varied greatly in different specimens, but most frequently these were arranged in a broad ellipse within which many others formed a second ellipse or were most irregularly disposed. Several zygospores were found in the same collection, but none with empty semi-cells attached. They were spherical and about 60 µ diameter, without spines. The surface bore many simple straight spines 11-15 µ long. It seems quite possible that these are zygospores of the numerous var. quebecense cells present.

            A pool of stagnant water in a large granitic ledge contained large numbers of another form of Xanthidium antilopaeum. The many cells examined are of very uniform appearance and represent a distinct variety. They are of medium size, about one and one-quarter times longer than broad, sinus at first linear, then divergent to a rounded basal angle. Apex usually straight, less frequently slight convex, infrequently faintly retuse, the lateral margins straight or slightly convex. Angles rounded, each furnished with a pair of stout upwardly curved (rarely straight) spines frequently yellowish-colored. In a few instances a third spines may exist between or lateral to one or both pairs of basal spines. Central thickened area brownish-yellow and circular or elliptical, and furnished with numerous scrobiculations which are variously arranged. Sometimes these are very faintly visible or even completely lacking. Vertical view elliptical with truncated ends, each bearing a pair of parallel or slightly converging spines. Side view of semi-cell subcircular. Length 74-80 µ; breadth (with spines) 87-95 µ, (without spines) 60-68 µ; thickness 45-48 µ, breadth of isthmus 24-36 µ; length of spines 13-16 µ. Distinct from other species and other varieties in relative dimensions, in its straight apical margin, and the disposition of the spines. This plant seems to have been first described in 1888 by W. H. Hastings, presumably in his local newspaper, as Xanthidium antilopaeum var.  truncatum. Soon after W. West described the same plant as X. Tylerianum (misquoted as X. Taylorianum) as synonymous. It would seem better to keep this desmid as a variety of X.  Antilopaeum; therefore it becomes Xanthidium antilopaeum  var. Tylerianum (W. West) Whelden comb. Nov. (Fig 17).

Arthrodesmus quadridens Wood is one which has frequently appeared in collection from Maine and has always attracted considerable attention, primarily because it seemed so different from all other species of the genus. Recently Prescott and Scott, with good reasons, have removed this alga from that genus, and established for it a new genus, Spinocosmarium. They note that the species S. Quadridens show “a great variation in the degree to which granules and processes are developed”. This is indeed so. However, collections vary greatly in this respect. Frequently one may examine scores of specimens in a single collection and find no obvious variation. In another collection from a habitat closely resembling the first, every specimen seems distinct in some way. The most conspicuous variation occurs in the spines which are so striking a feature of the lateral margin. These may be simple or once-furcate ; between cells in which all spines are simple and those in which all are furcate, every conceivable combination of simple and furcate spines occurs. In the furcate spines the two forks are usually nearly equal in size, but instances do occur in which one forks may be reduced sometimes to a degree where it become merely a minute tooth on one side of the spine. Infrequently spines are borne at the apical angles and are usually much smaller than lateral ones. Generally the spines occur singly, although occasionally two may be produced on angle. All specimens I have examined are alike in having a single large rectangular tubercle just above the isthmus. The many other tubercles vary greatly both in prominence and in number, especially in the lateral parts of the cells. In rare cases coarse pores occur in abundance and irregularly distributed in the wall between the tubercles. Generally this wall appears smooth. The cells were 33-42 µ long, 51-57 µ broad (with spines) and 33-40 µ without; the isthmus was 9-13 µ broad; the cells were 24-26 µ thick.

Three species of Staurastrum merit notice because of their zygospores. On three different occasions zygospores of St.  ptunctulatum Breb.  have been found in abundance, once in mid-May and twice in late summer. The most noticeable feature of these zygospores is the broad range in size, from 36 µ to 62 µ in diameter, the processes included. (Fig. 11.)

            In several shallow pools Staurastrum Rotula  Nordst. (Fig. 12.) is a species encountered frequently and generally in large numbers throughout the warmer months, becoming particularly common in August and September. During the entire period the rather large cells show a certain amount of variation ; the number of processes may be either eight or nine. These rays usually are quite straight, those of the two semi-cells being parallel. Not infrequently one finds specimens in which the processes are curved outward. The margins of the processes are in most instances coarsely crenulated, but occasional specimens are found with perfectly smooth processes. The verrucae which are so characteristic a feature of this species also vary, being usually rather large and bidentate, in other cases small and conical, and occasionally completely lacking. Some of the specimens have larger dimensions than those usually given, being 42-48 µ long, and up to 124 µ broad (processes included).

            Zygospores of this alga were found in very large numbers during August and early September of 1929. They were spherical bodies 36-43 µ in diameter, with many straight or slightly curved processes 28-32 µ long. In some zygospores the apices of all processes were armed with two or rarely there curved teeth ; in other zygospores the ends of all processes were simple and rounded ; in some, processes of each type occurred. The body of the zygospores was deep brown to black in color. Fig. 12 show there zygospores with different types of processes, and two cells, one with crenulated and the other with smooth processes. Infrequently zygospores of this species were found infected with a small undetermined fungus. In these the processes were generally much shortened (10-15 µ long), coarser than normal, or even unciform. Such infected zygospores were easily reconized as abnormal, even when the parasitic body was not distinctly visible.

            Staurastrum johnsonii var. depauperatum G. M. Smith (Fig. 13) occurs quite generally in this region, sometimes in abundance, together with the species. Occasional specimens of zygospores of the present species were found. They were spherical bodies of brownish color, 28-32 µ in diameter and provided with 12-15 simple straight processes 16-20 µ long.

            Disregarding purely taxonomic problems and those dealing with the life-histories of algae, interest in this group of plants has centered around three main questions, their distribution in both a local and a broader sense, the variations that they exhibit and possible explanations of them, and the formation of sexual stages, with some attention being given to the periodicity of their existence.

            The appearance of sexual stages and especially of zygospores in the desmids, is often a rare occasion. To record their occurrence, therefore, seems ever desirable, the more so when notes on any unusual circumstance attend this; with the accumulation of such cases an understanding of some of the causes leading there to may be had. Certainly my own observation on zygospores, far more numerous than those recorded above, lend no support to any statement that any one season favors their appearance. Frequently one finds a collection in which any different species of the algae present are fruiting freely, thus sugesting that this event is a consequence of external factors. The collection in which the zygospores of Staurastrum Rotula were so abundant is of this sort, for in this ten different algae, including eight desmids, were forming zygospore. In other cases, large number of algae may be present , and only one fruiting. Collection in which a dozen species of Closterium are abundant may show only one forming zygospore. It might then be suggested that an internal factor might be operating.

            The question of occurrence, or favorable habitats, may be briefly mentioned. Everyone who has given serious attention to collecting algae knows that there are problems involved, in deciding just where collecting may be best. Nor can any rule be given for this. A collection may be very poor in number and quantity, yet show rich variations in the material that is present. Apparently identical habitats may show entirely different result, one spot yielding abundant material while one nearby is almost barren. Variations of this kind may be found in two collections made in a monotonously uniform habitat and only a foot apart. It would seem that oftentimes the algae maintain a remarkably fine adjustment to some factors in their environment or within themselves. All too frequently algae, especially desmids, may disappear from some place with startling abruptness, not  trace remaining in a habitat which twenty-four hours before gave very rich collections.

            The question of variations in algae and the causes of them has attracted considerable attention. Jacobsen (1875) was one of the first to consider the nature and causes of variations so frequently observed in desmids. He advanced several possible explanations and note the wide geographical range of the variations. De Wildeman (1887) paid attention to this question, brought together may cases of  variations noted by previous workers and concluded that . . . “ce ne sera que par une etude approfondie faite sur de nombreux materiaux de diverses provenances que l’on pourra arriver a donner, a chaque espece, la place qui lui convient dans la serie et a supprimer toutes les especes don’t la creation est basee sur der caracteres secondaires.” Later de Wildeman (1895) noted the frequency of occurrence of variations in the genera Euastrum and Micrasterias. Cushman (1907) found the species of these so called variable, and remarked that “as many of these so called varieties are often seen forming one semicell of a specimen, the other semicell of which is typical, it seems hardly wise to recognize them as good varietes.” Johnson (1894), Stange (1908), Playfair (1910), Ducellier (1914, 1915, 1917, 1918), Woronichin (1926) and Huber-Pestalozzi (1913) are among the many who have given considerable attention to the occurrence and extent of variations under natural conditions, and offered various explanation as to their causes. More recently Lefevre (1939) has studied the problem both in nature and more especially in cultures. His extensive experiments on several genera and species of desmids lead him to conclude that anomalies and monstrosities appear much more frequently in cultures than in natural habitats. He is led to state that “Observations based on material grown in culture can never replace material observed in nature, but will serve only to supplement these and may give proof to matters otherwise left very doubtful.”

            The notes on variations recorded above are based on materials from natural environment. They lead to certain observations. Monstrosities such as those in Eaustrum and Cosmarium  do occur infrequently and in many cases at least see to be accompanied by, if not indeed a consequence of, attack by a parasitic organism. It is quite possible that in such abnormal forms as those of Micrasterias (Fig. 15) a parasitic organism is present, but in a stage the presence of which is not yet apparent. For certain it is that this genus is frequently infested with parasitic organism. Possibly such abnormal forms occur only if the parasite enters just before division of the host begins, or in its early stages.

It has frequently been stated that the many variations in size, form, ornamentation, and cell contents occur much more frequently in certain genera. Undoubtedly this is true. It is also a fact that in many cases the very nature of the cell makes it difficult to observe variations—small smooth species of Cosmarium cannot offer as much in the way of variety as ornate ones. Where obvious variations do occur it is seldom possible to ascribe to them definite causes. Many factors outside the cell come to mind. Abrupt changes in temperature, and large fluctuations in the amount of substances dissolved in the water have been frequently mentioned. Yet when one observes what happens in two small nearby pools, or examines two collections from point near one another in a single pool, where great uniformity in the species in the other collection, one concludes that such a factor cannot always operate. Nor do they seem adequate to explain all observations. Many things indicate that there is within the organism themselves something which may lead to the appearance of variations, and that this together with other external factors operate together perhaps in very subtle ways to bring about the morphological changes which one observes. Only through observations accumulated slowly, and carefully supplemented whenever possible with observations on controlled cultures, can a solution of these problems of algal behavior be hoped for.
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