No. 506] KELPS AND RECAPITULATION TllFJUO DO 



Leaving these questions for the present, we may ex- 

 amine the facts in the development of our kelps, to as- 

 certain whether these juvenile forms repeat only other 

 juvenile forms or whether they go farther and approxi- 

 mate the adults of their ancestors. Nothing could be 

 more instructive on this point than the figure of the 

 young plant of Lessoniopsis printed beside the adults 

 of Renfrewia (Figs. 15 17). In all external characters 

 save the characteristic spots of Lessoniopsis and the re- 

 productive maturity of Renfrewia they are in essentials 

 identical. The structure of the holdfast is particularly 

 interesting. Both are simple discs strengthened by pri- 

 mary hapteres originating through the uneven growth of 

 the disc itself. The young of other kelps might have 

 been used for this comparison, e. g., Hedophyllum (cf. 

 Fig. (5), but Lessoniopsis retains these primitive char- 

 acters at a larger size than the others and therefore 

 lends itself more easily to photography while its deter- 

 mination is at the same time certain because of the spotted 

 lamina. In Pterygophora the correspondence is in all 

 respects just as complete, see MacMillan's figures 

 ( '02). There persists for a considerable period the sim- 

 ple lamina with the short stipe on the primitive disc 

 and its primary hapteres for holdfast. After the sec- 

 ondary hapteres have appeared and until the midrib has 

 been formed the young plants are very difficult to dis- 

 tinguish from those of Lamiuaria saccharina which grows 

 in the same locality. These again are in all respect >. ex- 

 cept size and reproductive maturity, like the adult plants 

 of their species. ^ ^ fl 



facts without comparing these non-correspondent stages 

 of Lessoniopsis and Renfrewia, and of Pterygophora am 

 Renfrewia and Laminaria. The simple facts of the case- 

 are that Lessoniopsis and the others when still very small 

 pass through a condition which must be considered with- 

 in the generic limits of Renfrewia. Conversely, the 

 adults of Renfrewia do not differ in any important char- 



