1G8 BOTANICAL MAGAZINE. [Vol. xvii. 



TJialassiophyUum and Arthrotliainnus have hitherto been incompletely 

 studied. The author could happily trace the stages of the development in 

 the both genera during the stay. On returning home from the trip, I was 

 struck with curious coincidence upon reading the excellent work newly 

 published by Setchell and Gardner.^ ^ They gave precise description on the 

 development of Thalassiopliyllump which I expected to write, and reformed 

 the previous knowledge relating the plant. Nothing might be added to 

 their description about the transformation of the external character through 

 the development of the plant. A few words, however, shall be necessary 

 to describe about the development of Arthrotliamnus, on which, as far as 

 I could refer to, no one seems to have touched yet. 



At the first stage of development the lamina is linear, 8-12 cm. long 

 and 2.5-3.0 cm. wide, attenuated tovv^ard the base which ends in a cylindrical 

 stipe. Tho stipe measures 1.5-2.0 cm. in its length and has a simple 

 holdfast. 



The lamina expands into a thin wide blade in the next stage, the 

 upper portion gradually wearing awa}'. The stipe increases in its thickness 

 and number of thick rhizomes are given 7'ise at the upper portion of the 

 primary holdfast. The length of the stipe is thus greatly diminished, 

 (flg. 10). 



A limitted portion of the margins close at the transition region is 

 scrolled inside for one turn. The scroll is not loose spiral roll but rather 

 a sort of hemming without any descriminable space inside. The apical 

 portion of the inner edge of the scroll develops into a short cjdindrical 

 stem which gently expands into a narrow lamina (fig. 10). 



The primary lamina disappears in this stage leaving the wide sinus 

 between the new stems. The scar of the worn lamina traverses along the 

 sinus and turns from the outerside to the innerside around the base of, 

 each new stem. (fig. 11). 



The newly formed or the socondary lamina is almost always unsym- 

 metrical, especially at the beginning of its growth. This is due to the 

 greater rapidity of the growth at one — in majority of cases, external — side 

 of the lamina. As the plant grows larger the stems begin to increase 

 their thickness and the rhizomes begin to appear as the stout processes 

 around their basal parts, (fig. 11), 



The secondary lamina develops further until it retained the proper 



1. Algae of N.W. America. 



2. p. 267. 



II 



