THE 



AMERICAN NATURALIST 



Vol. XLIJI January, 1909 No. 505 



JUVENILE KELPS AND THE RECAPITULATION 

 THEORY. I. 



PROFESSOR ROBERT F. GRIGGS 

 Ohio State University 



I. The Development op Cebtain Kelps 

 A. Renfrewia 1 



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 Ren- 

 frew, 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, how- 

 ever, 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 Set- 



