No. 505] KELPS AND RECAPITULATION THEORY 1 5 



to which Lessoniopsis belongs, is characterized by the re- 

 peated splitting of the original unbranched lamina till the 

 plant comes to have a cluster of many leaves. The 

 method of this branching is peculiar to the kelps. In- 

 stead of forking at the tip or sending out a new shoot as a 

 lateral proliferation, the branching begins in the trans- 

 ition region between the stipe and the lamina and ex- 

 tends upward until it reaches the tip of the lamina, thus 

 splitting it, while the stipe is divided, to a greater or less 

 extent in the different genera, by the downward extension 

 of the same process. This method of branching is the 

 necessary consequence of the position of the meristem, 

 which is situated at the junction of lamina and stipe, so 

 that all new growth is intercalated between the older por- 

 tions of both. It is obvious, therefore, that any new 

 structure, such as a branch, must originate in this region 

 of growth. 



In Lessoniopsis the first indication of branching ap- 

 pears in a slight depression in the midrib on each 

 side of the lamina at the transition region. These de- 

 pressions or pits enlarge and deepen until they meet and 

 form a perforation almost exactly at the base of the 

 lamina. It will be readily seen that if the split extended 

 uniformly upward through the midrib, it would result in 

 two unsymmetrical falcate laminae each with a rib along 

 its inner side. This, however, is not usually the case, for 

 new tissue forms between the divisions of the midrib and 

 soon duplicates on the inner side the outer edge of the 

 lamina (Fig. 24, a). Thus each of the new lamina? is ap- 

 proximately symmetrical with respect to its midrib. In 

 the stipe the branching is carried far enough to involve 

 the whole of the meristem, so that future lengthening is 

 almost completely confined to the stipes of the branches. 



Before the new laminae have completely separated there 

 usually begins to appear at the base of each, the second 

 split, which is carried to its completion in the same man- 

 ner as the first. Thus branching continues again and 

 again so long as the plant lives. Since all the splitting is 

 dichotomous, the result should be a flat fan-shaped plant, 



