1922] Skottsherg: Notes on Pacific Coast Algae 431 



two types of apical growth, the hypoglossum-tyipe and the sinuosa- 

 type. The difference between them, as described and illustrated by 

 Nienburg, may be summarized as follows. Both have a central axis 

 with a primary top-cell and regular opposite branches, each ending in 

 a secondary top-cell. In the liypoglossum-type these branches of 1. 

 order carry, on their external side, branches of 2. order, each ending 

 in a tertiary top-cell (fig. 2). In the sinuosa-tyipe such top-cells do 

 not become developed : the cells of the branches of 1. order are divided 

 by length and cross-walls, but we do not find the regular arrangement 

 of branches second order as in the other type. Thus the appearance 

 of the growing apex becomes quite different in the two eases. To the 

 Jiypoglossum-type also belong D. sanguinea and alata, to the sinuosa- 

 type, D. Lyallii. 



It was easy to see that D. quercifolia Bory as well as the Californian 

 species belong to the sinuosa-type. But when it came to the analysis 

 of the mode of development I could not bring my results in accordance 

 with Nienburg 's scheme. Anybody comparing my figure 3 with his 

 figures 16 and 44 will discover the difference. And as the plasma 

 connections designed by the writer were observed on alcohol material, 

 while Nienburg 's analytical scheme is a construction, I concluded that 

 the latter was not correct, or that, after all, D. quercifolia differed 

 from the sinuosa-type. I had a discussion on this matter with Pro- 

 fessor H. Kylin, who has occupied himself with an examination of 

 D. sinuosa. He kindly informed me that Nienburg 's explanation of 

 the growth is partly incorrect and that, in fact, the development is the 

 same in sinuosa and quercifolia. Nienburg 's types will stand, their 

 systematic importance will prove to be very great, but the main point 

 of difference seems to have escaped his full attention. In the hypo- 

 glossum-type, the cells of the main axis keep pace with the develop- 

 ment of the branches of 1. and 2. orders by getting elongated, while, 

 in the simiosa-type, they become divided by intercalary cross-walls 

 (a well-known fact), and the intercalary cells thus formed develop 

 short, few-celled branches which become inserted between the branches 

 of 1. order. This system of intercalary branchlets is dotted in figure 

 3. The same mode of growth is repeated in the branches of 1. order. 

 Thus it is easy to understand why the beautiful cellular architecture 

 of a Z>. hypoglossum is lost in D. sinuosa or quercifolia. In the Cali- 

 fornian species, owing to the dry material, no plasma connections were 

 distinctly visible, but a comparison between figures 3 and 4 will show 

 that the development is the same in both cases. 



