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presence the plant is practically possessed of a new basal meristem supplementing and to a certain extent supplanting the primary meristem. Once established in a favorable situation, a plant may therefore maintain itself indefinitely, casting off old branches and developing new ones continuously.

D. Hedophyllum Because of the close similarity of the young stages of Egregia and Hedophyllum sessile it will be of interest to add a short description of the latter. It has already been the subect of considerable study by Setchell, who has published (05) a discussion of its development well illustrated by figures. His paper, however, was written from another point of view than the present, namely, the relationships of Hedophyllum sessile to the other species of Hedophyllum and to Agarum and Thalassiophyllum. Since from this standpoint the very young forms of Hedophyllum are not important, Setchell was not particular to obtain plants less than about 5 cm. in length. But for a comparison with Egregia the younger forms are of the most interest. This species2 is extremely abundant at the Minnesota Seaside Station, outnumbering in individuals any other kelp present on that coast. It grows at the highest level occupied by the kelps, and in various situations as regards wave action.

Very young plants of Hedophyllum are difficult to distinguish with any certainty from Egregia and from the various species of Laminaria growing in the same locality. Hedophyllum is, however, much more abundant in adults and juvenile forms, and as the specimens selected were taken from beds composed mostly of Hedophyllum, the probabilities are greatly in favor of a correct determination. The youngest plant (Fig. 5) measured approxi

? Though Puget Sound is given as the southern limit of the other American species, Hedophyllum subsessile, I have been unable to satisfy myself of its occurrence at Port Renfrew. Two distinct series of juvenile forms are, however, represented there, one with a narrow blade like those which Setchell figures, and, as here described, another with a very broad, cordate blade even when very young. What the relations of these may be to the adult plant I have not yet fully determined.

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Figs. 37-42. Hedophyllum, series of young plants showing the gradual obliteration of the stipe by the broadening of the transition region, and the origin of new hapteres higher and higher up the stipe. Four fifths natural size. mately 2.3 mm. in length and the margin of the primitive disc was nearly smooth. The edge of the lamina was only one cell in thickness, but there were evidently several layers in the middle region and toward the base. In a specimen 6.5 mm. long the holdfast had become distinctly crenate around the edges and the one-layered lamina had disappeared. The crenations had become much more pronounced and had assumed the characters of primary hapteres in a specimen 10 mm. long (Fig. 6).

By the time the plant reaches the length of an inch its determination is not difficult. A specimen 28 mm. long (Fig. 37) will serve for comparison with the youngest Egregia described. The lamina is narrower and longer than in that plant; the holdfast has not as yet developed secondary hapteres and the stipe is shorter. Though the stipe always remains short, it usually becomes longer than is shown in this plant (about 5 mm.). The narrowness of the lamina is characteristic, but is not sufficiently marked at stages earlier than this to render diagnosis easy.

Soon after this stage secondary hapteres begin to appear above the primitive holdfast. Though they arise in circles as in the other kelps, they usually develop quite unevenly in the young plant, some members of the circle becoming long, while others are yet mere knots on the stipe. When a length of about 8 cm. is reached the stipe begins to thicken and flatten. The transition region, which has been sharply marked off, becomes less and less distinct and the plant comes to consist of a lamina with a cuneate base anchored by the holdfast (Fig. 42). This condition sometimes persists until the plant has reached a considerable size. More usually, however, the broadening continues and quickly brings about the adult condition.

When mature (Fig. 43), Hedophyllum sessile becomes a broad, cordate, sessile plant anchored by a mass of hapteres at its base. Its lamina is torn to ribbons like a digitate Laminaria, so that it may resemble one of the kelps with true branching. The hapteres arise in circles one above the other higher and higher up on the stipe

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Fig. 43. Hedopnyllum, medium-sized plant showing the cordate lamina torn by the waves. A fully mature specimen would be a rosette so dense that its structural relations could not be made out. One fifth natural size.

until they obliterate it and even come to grow out from the lamina itself. Thus there arises a thickened basal portion of the lamina which forms a conical holdfast, as in the other kelps, while new circles of hapteres may be seen on its upper edge, growing out from the undifferentiated lamina. By this process the holdfast region extends beyond the bases of the segments of the lamina so as to give the old plant the appearance, not of one, but of several independent lamina springing from a common holdfast. Considering the similarity of the young plants to Egregia, the divergence of the adults is very striking.

(To be concluded)

THE LARVA AND SPAT OF THE CANADIAN

OYSTER

J. STAFFORD, M.A., Ph.D.

MONTREAL

I. THE LARVA In the summer of 1904, at Malpeque, Prince Edward Island, on behalf of the Canadian Marine Biological Station, I undertook to gather what information I could upon the life of the oyster from the time it becomes a distinct bivalve veliger to the time when it is recognizable by every oyster fisherman as a spat oyster.

Brooks, of Johns Hopkins University, Baltimore, to whom belongs 'the immortal glory of having discovered that American oysters are unisexual and that artificial fertilization of the eggs and rearing of the larvæ are possible, had worked out the spawning, fertilization, segmentation, gastrulation and organization up to the earliest microscopic free-swimming bivalve veliger, and there was no lack of literature on oyster culture beginning with macroscopic oyster spat of, let us say, the size of one's thumb-nail. But the intermediate stages, mostly microscopic, seemed to be scarcely, if at all, known, and there were many questions as to the time and place where they might be found as well as to their anatomy and comparison with other genera which required investigation.

The possibility of raising young oysters from eggs and keeping them alive without admixture with other individuals or other species until one had seen the whole series of continuous transformations into the adult seemed next to impossible. I chose rather to learn to recognize the larval oyster in plankton collections, a method which had apparently received no attention. I

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