FOR the preparation of a former article (Griggs, '06) on Renfrewia the writer had no very young plants, but during the summer of 1907 he was enabled to collect a full series at the Minnesota Seaside Station, Port Renfrew, B. C. This material is of interest for the study of the development of this, the most primitive of the kelps in comparison with the more complex forms. The smallest specimen found, which measures a trifle less than 4 mm. (Fig. 1), is not certainly determinable. But one 13 mm. long (Fig. 2) had already developed a peculiar swelling of the basal region which characterizes the young plants. The primitive disc of most kelps and of Renfrewia up to this age is rather flat and sharply separable from the stipe, which ascends cleanly without tapering from the top of the disc. In Renfrewia, however, the basal region of the stipe (the region which in other kelps develops hapteric outgrowths) increases in size. As the plant grows this swollen region becomes more prominent till in plants 8 cm. long (Fig. 11) the 1 Since publishing the original account of Renfrewia parvula in 1906 I have found that it is apparently conspecific with Setchell's ('01) Laminaria ephemera earlier described from the California coast. Accordingly Setchell's name replaces mine and the plant becomes Renfrewia ephemera (Setchell). Cf. Setchell, '08 b. FIG. 1. Renfrewia, 4 mm., shading shows the position of single and manylayered areas in the lamina, holdfast without basal cone. FIG. 2. Renfrewia, 13 mm., lamina many-layered throughout basal cone beginning to appear. FIG. 3. Lessoniopsis, 1.1 mm., lamina about four-layered, spots already shown in the cortex, holdfast not developed, plant apparently anchored by filaments. FIG. 4. Lessoniopsis, 2.3 mm., spots in the lamina larger and more evident distally, but still small near the transition region, indicating that growth is already localized, primitive disc developing at base of stipe. FIG. 5. Hedophyllum, 2.3 mm., showing the much-lobed primitive disc. FIG. 6. Hedophyllum, 10 mm., lobes of primitive disc grown into the primitive hapteres. holdfast is an almost straight-sided cone 5 mm. in diameter and of about equal height. Though apparently insignificant this character makes it easy to pick out Renfrewia from other kelps while yet very small. So far as the writer is aware it is not present in any other kelp. After the plant has reached about a decimeter in length the basal cone ceases to increase and later is lost in the growth of the stipe (Fig. 12). At the same time the disc begins to enlarge and spread out on the substratum, giving a firmer hold for the increasing lamina above. This enlargement is clearly in the region of the primitive disc and not in the conical basal swelling above, which remains part of the stipe. These two tendencies of growth working together usually cause the sharp distinction between the holdfast and stipe to reappear, and in plants more than 15 cm. long the conical base is seldom prominent (Fig. 13). In adults the disc becomes very flat and thin by its continued extension (Fig. 14). FIGS. 7-11. Renfrewia, series of young plants showing the development of the basal cone. Four fifths natural size. FIGS. 12-13. Renfrewia, older plants showing the gradual disappearance of the basal cone with increase in size. Four fifths natural size. FIG. 14. Renfrewia, base of an adult plant, fruiting area extending over almost the entire lamina, its margin indicated by shadows here and there, holdfast showing primitive hapteres. Four fifths natural size. Some speculations as to the nature and significance of this cone may be of interest. Of all the kelps Renfrewia and Cymathere are the only ones in which the mature holdfasts are restricted to the primitive disc region. In the development of the latter genus, as traced by the writer ('07), there is no indication of such an organ as can be seen by an inspection of the figures then published. Phyllaria and Saccorhiza differ in their holdfast characters from all the other genera. Instead of putting out hapteres directly from their stipes they develop bulbous "rhizogens" which form ring-like collars around the stipe. From these the hapteres are formed by unequal growth along their margins. Though the rhizogen in both genera is separated from the primitive holdfast by a distinct interval on the stipe, it is essentially similar to the basal cone of Renfrewia which we may consider as an incipient rhizogen. This would indicate some leaning of Renfrewia toward the Phylariatæ; but its paraphyses are of the typical clavate form not at all similar to the linear ones of that group. Whether this basal cone is a nascent organ representing the beginning of the holdfast or is a vestige of a Saccorhiza-like rhizogen is a puzzling problem. At some stage in their history the rhizogens of Saccorhiza and Phyllaria probably passed through this condition and remained for a longer or shorter period without further development. On the other hand, the obscuring of the cone in Renfrewia when adult might suggest a vestigial organ. Perhaps the best hypothesis is that Renfrewia was cut out from the main advancing phylum of the kelps, isolated and fixed, at the stage where the tendency to form a secondary holdfast was just beginning to manifest itself. The tissues of the many-layered lamina of Renfrewia are apparently acquired after the fashion of other kelps, but in Renfrewia the many-layered lamina begins its development in smaller plants than in the Phylariatæ including Cymathere. Even in the smallest specimen (Fig. 1) there is only a small portion of the one-layered blade remaining around the edge of the lamina. In the |