118 Rhodora [JUNE 
New England coast, the writer has found that the summer form is 
usually ample, with ruffles and rows of indentations fully developed ; 
but in August a change takes place and this summer blade is replaced 
by a winter blade which is perfectly plane and devoid of both of these 
features. Again, in the spring, this plane blade is replaced by the 
ruffled and indented form, and it is possible, accordingly, to find at 
these seasons fronds which show blades of both kinds in varying pro- 
portions. This seems to be a sort of seasonal dimorphism. 
The duration of the species of Laminaria has never been carefully 
investigated; it probably varies very much among the species of the 
genus. JZ. /ongicruris is credited with being an annual plant, while Z. 
saccharina is biennial at least, and is probably perennial. Z. digitata 
is certainly perennial and has rings in the lower portion of the stipe 
which are probably rings of growth. Z. stenophylla and Z. intermedia 
seem to be the annuals among our digitate Laminaria, while Z. platy- 
meris is certainly perennial. 
The perennial species all show the phenomenon of the renewing of 
the blade, due to a cessation of the growth during the latter part of 
the winter, the thickening of the tissues of the blade and usually the 
formation of sori. In the spring, the active intercalary growth is re- 
sumed by the inner tissues. "The result is that the old thick, fruited 
blade is carried up on the summit of the new thin, as yet usually 
sterile blade, and the constriction between the two as well as the dif- 
ference in texture between the two blades, makes this a very striking 
phenomenon in the majority of species. The digitate forms with 
mucilage glands in the stipe show the renewal in a much more striking 
fashion than do the digitate species without the ducts in the stipe, as 
Foslie (1884, pp. 26—28 and pl. 1, f. 1, pl. 5, f. 4, pl. 4, f. x, pl. s, f. 1, 
2, pl. 10, f. 3-10), has shown. A similar difference exists in the 
cases of Z. digitata and Z. platymeris of the New England coast. In 
the perennial (or biennial?) form of the .SzmpZices group, the renewing 
of the blade in the spring is equally pronounced, the plane thick blade 
of the winter being replaced by the thin, ample, ruffled, and indented 
blade of the spring and summer. In these forms, an almost equally 
pronounced renewing takes place in the early or later autumn, as 
mentioned above, when the thick, ruffled, indented and often fruited 
blade of the summer is replaced by the fairly thick plane blade of the 
early winter. The renewing at these seasons is found even in young 
specimens (cf. Foslie, loc. cit., pl. 10, f. 3-10). 
