No. 505] KELPS AND RECAPITULATION THEORY 13 



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 Kenfrewia, 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 mar- 

 gin. In places the localization had become sufficiently 

 pronounced to give rise to definite primary hapteres ex- 

 actly as described by MacMillan ( '99) for young plants 

 of Nereocystis and by the writer in the adults of Een- 

 frewia 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 indi- 

 cated 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 pro- 

 nounced than any other portion of the rib. 



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



