13 mm. specimen (Fig. 2), the whole lamina is many layered without any signs of the one-layered portion persisting around its edges. Apparently the embryonic lamina is almost wholly transformed into the adult blade. Like the adult, these young plants are light colored and delicate in texture. They are narrowly elliptical in shape, cuneate at the base and rounding to the apex when not badly abraded.

Except for the basal cone of the stipe young plants 15 mm. long in all characters are like the adult. The adult is larger but the proportions remain the same. Even in the histology there is probably very little differerence, for, as described below, Renfrewia develops very imperfectly the complex tissue system which characterizes the higher kelps. What differentiation of tissues appears is probably present long before adult size is reached. Were it not for their reproductive maturity it would be difficult to demonstrate that the adults were mature and not merely larger juvenile forms (Figs. 16, 17); and they have been mistaken by competent observers for juvenile forms of some other kelp.

B. Lessoniopsis

Lessoniopsis is a monotypic genus ranging along the Pacific coast from California to Vancouver Island. It was founded by Reinke ('03) to receive Lessonia littoralis Farlow and Setchell (see Setchell, '03) which differs from Lessonia in the marked dimorphism of the laminæ, as described below.

The juvenile forms of Lessoniopsis are extremely abundant during July and August at the Minnesota Seaside Station. They grow in clumps of many individuals of all ages. As often as not these clumps start upon the stipes of other kelps, so that one can obtain many hundred specimens simply by cutting off a few old Laminaria stipes. Though the mature plants are often single, it is not at all unusual to find several large plants fused together, as was noticed by Reinke. The reason for this habit of growth of the sporelings is a matter of some in

terest. There is no difference, as far as the writer is aware, between the fruiting habits of this and other kelps. In quiet water the fragments of any fruiting lamina torn off by the waves might lie undisturbed on the bottom and the spores might germinate close to the point of liberation. But this kelp is a cumaphyte growing exclusively in the strong surf, and it is in surf-scoured situations that the young plants are found best developed. This would lead one to look for some method of basal branching or possibly budding of new laminæ from the holdfast, as is known in a few kelps which have "rhizomes." But though hapteres and stipes are occasionally so completely grown together as to appear branches of one plant, no evidence of such branching in the young plant has been observed and the writer must conclude that the clusters are due to starting of many spores at one point.

The young plants forming these clumps are thickly splashed with checks of dark brown on the lighter color of the body of the lamina. This is most conspicuous in plants about 10 cm. long and is clearly brought out in the photographs (Figs. 15, 21). As they grow older the spotting tends to disappear, but traces of it can usually be found in specimens of any age. No other kelp of the region is similarly marked except Pterygophora, in which the spots when present are much less distinct. As this appearance arises very early it is of the utmost service in identifying the plants while yet too young to have developed any characters of the adult.

The smallest specimen found (Fig. 3) measured about 1.1 mm. in length. It was attached to the hapteres of another plant of the same species twenty or thirty times as long. When loosened from its hold it came away with a mass of filamentous material which completely enveloped its base. In this tangle there was a considerable portion of foreign matter; but the appearance of the finer strands was that of a protonema-like felt organically connected with the young kelp which seemed to spring from it like the gametophore of a moss. On teasing this away it was seen that the primitive disc had not yet developed.

FIG. 15. Lessoniopsis, 30 mm., lamina showing the characteristic spots, midrib just beginning to appear, holdfast formed by conspicuous primitive hapteres.

FIGS. 16-17. Renfrewia, adult, showing similarity to Lessoniopsis when young, fruiting area covers almost the entire lamina in Fig. 16, but in Fig. 17 occupies only a small area at the base and hence clearly discernible, spots in Fig. 16, due to epiphytic algæ. About one half natural size.

The base of the stipe was but slightly larger than the portion above and gave off a large number of filamentous processes, some of which seem to have pressed against the substratum, while others apparently connected with the filaments around the base. Notwithstanding its small size this specimen had a well-developed stipe about a dozen layers of cells in thickness. The internal cells are considerably elongated, though not, as far as can be seen by focusing, differentiated into a pithweb. The lamina was already several cells in thickness even at the edge. Since it was but little frayed, it hardly seems possible that there could have been any remnant of the one-layered lamina which had not been transformed into the many-layered adult blade. In this respect Lessoniopsis would stand at the opposite extreme from Cymathere, in which a large portion of the embryonic lamina is not changed, but continues to grow and persists until the plant is more than 20 cm. long.

The next larger specimen (Fig. 4) measures 2.3 mm., but its true length must have been about 5 mm., for it is sharply truncated a little above the base of the lamina. The holdfast of this specimen was enlarged to form a fairly well developed primitive disc, the base of which was, as in the first specimen, more or less imbedded in a mass of filaments apparently belonging to the kelp. The lamina was much thicker and the spots were seen to be in two layers, one on each side, just beneath the epidermis. In the smaller specimen (Fig. 3), where one spot overlapped another, the two layers could also be made out, but the difference in focus was so slight as to make it appear that they lay in contact, indicating that the lamina was four cells in thickness. In the larger specimen they were separated by a considerable interval which indicated a decided development of the pithweb and cortex. Toward the extremity of the lamina the pigmented spots were very dark and most of them were considerably elongated. They still consisted, however, for the most part, of single cells. Farther back in the transitional region, they were lighter in color, round and more

like those of the first specimen (see Fig. 3). This shows that the region of growth had been definitely localized as a meristem at the base of the lamina (as in the mature plant), while further out in the lamina growth was taking place mainly by the enlargement of cells already formed. From this point on the development of the species was illustrated by many specimens of all ages. The first marked change was the enlargement of the primitive disc. In a specimen 30 mm. long (Fig. 15) the disc had reached a diameter of 4 mm. At this stage it bears a striking resemblance to that of the adult Renfrewia, being very flat and closely appressed to the substratum. As in that genus, the growth which causes the enlargement becomes localized in certain regions, giving the disc a crenate margin. In places the localization had become sufficiently pronounced to give rise to definite primary hapteres exactly as described by MacMillan ('99) for young plants of Nereocystis and by the writer in the adults of Renfrewia and Cymathere. These primary hapteres are of course all restricted to the primitive disc. Soon after this stage the secondary hapteres begin to arise around the base of the stipe and become very abundant, quickly obliterating the primitive holdfast. The age at which branching and differentiation of the midrib appear varies greatly. Sometimes the plant may reach a length of 80 mm., with only the beginnings of the midrib and of the splitting to form the first branch (Fig. 21); while in one plant of 160 mm. the perforation of the midrib for the branch had only just been accomplished (Fig. 22). On the other hand a specimen (Fig. 19) measuring only 18 mm. showed the position of the perforation plainly marked out. The first appearance of the midrib is indicated by two straight lines extending from the transition. region up into the lamina (Fig. 20). The lamina between them grows thicker and takes on the characters of the midrib, which gradually extends toward the tip. But usually for a long time the two edges are more pronounced than any other portion of the rib.

As is well known, the whole subfamily, the Lessoniata',