No. 505] KELPS AND RECAPITULATION THEORY 9 



13 mm. specimen (Fig. 2), the whole lamina is many lay- 

 ered without any signs of the one-layered portion persist- 

 ing 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, cune- 

 ate 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 diff- 

 erence, for, as described below, Renfrewia develops very 

 imperfectly the complex tissue system which character- 

 izes 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 ma- 

 ture 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 Lessoma httornh* 

 Farlow and Setchell (see Setchell, '03) which differs from 

 Lessonia in the marked dimorphism of the laminae, as de- 

 scribed below. 



The juvenile forms of Lessoniopsis are extremely 

 abundant during July and August at the Minnesota Sea- 

 side Station. They grow in clumps of many mdn i«iuai> 

 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 Lammana 

 stipes. Though the mature plants are often single, it is 

 not at all unusual to find several large plants fused to- 

 gether, as was noticed by Reinke. The reason for this 

 habit of growth of the sporelings is a i 



matter of some i 



