2-lG Howe : Phycological studies 



that species, as well as specimens in herb. British Museum and herb. 

 Mus. Paris., distributed by Maze or by Maze and Schramm ^s Ap- 

 johnia tropica Crouan, all maintain the peculiar habit of growth 

 which reminded Agardh of Chordaria flagelUformis [I. c. p. 103). 

 The most frequent mode of branching hi 5. rigidns is, on the whole^ 

 the dichotomous, and dichotomy, so far as we have observed, does 

 not occur in S. tropicus. Occasionally, in 5. rigidns^ a fragment in 

 which dichotomies are rare or perhaps wanting and lateral prolif- 

 erations are numerous, like that illustrated in figure 2, may bear a 

 certain resemblance to 6". tropiats, but this resemblance, we be- 

 heve, is illusory, 



Halimeda 



and H, Ttina, The cell-walls of S. tropicus are comparatively 

 thin, measuring only 3-1 5 /i in thickness and the axes of the 

 much elongated flagelliform branches are typically two or more 

 cells broad, except at the extreme apices, while in 5. rigidns the 

 main branches are of a single series of cells for the greater part of 

 their length ; in S. tropicus^ the ultimate lateral branches are rather 

 uniformly and radially developed, in 5. rigidns they are somewhat 

 secund or very irregular in length and position ; the peculiar 

 mammillosities on the transverse walls, often conspicuous in 5. 

 rigidus^ though not always present, we have never observed in 

 ^. tropicus. 



In our earlier studies of Siphonocladiis rigidns we had be- 

 lieved we saw the formation of zoospores and pores for their escape 

 through the wall of the cell, but did not succeed in finding such 

 when the time came for drawing up the description. Cysts, how- 

 ever, are of common occurrence, and these may arise either by 

 the separation and rounding off of the individual cells within the 



common filament sheath or by the endogenous division of these 

 cells and the formation of new walls. The cells of the filament 

 in the ordinary vegetative condition are rather easily separable 

 from each other within the common filament sheath. Fig. 10 

 show^s the result of applying pressure to the cover-slip above a 

 filament-apex which had previously appeared transversely septate. 

 A curious and noteworthy feature of Siphonocladns rigidns is 

 the apparently constant presence of the delicate hyphae of a i^^'Ci' 

 gus (?) closely appressed to its surface. These hyphae are van- 

 able in abundance, but we have never seen a branch or even a 



