SPHACELARIALES (ISOGENERATAE) 157 



strengthened multiseriate filaments, Sphacella perhaps being one of 

 the more primitive members of the group with a non-corticate 

 monosiphonous axis. 



*Sphacelariaceae : Sphacelaria (gangrene). Fig. 108. 



The plants are filamentous with hypacroblastic branching in 

 which the cell below the apex cuts off two branch initials opposite to 



G E 



a 



Fig. 108. Sphacelaria. A, plant of S. cirrhosa ( x i). B, apical cell (a) of 

 S. cirrhosa. C, S. cirrhosa, origin of hair (h). a = apical cell. D, hair at older stage; 

 <2 = apical cell. E, apex of thallus of S. plumigera showing branches, b; single 

 segment {s), which later divides into upper {us) and lower {Is) segments ; a = apical 

 cell. F, origin of branch, b. G, bulbil of S. cirrhosa { x 52-5). H, unilocular 

 sporangia, S. racemosa. I, zoospore of S. bipinnata { x 1200). J, K, germinating 

 spore of S. bipinnata (X1200). (A, original; B-G, after Oltmanns; H, after 

 Taylor; I-K, after Papenfuss.) 



each other, although in some cases the initials may remain dormant. 

 The plants grow attached to stones or other algae by means of 

 basal disks or rhizoids that have spread down from the lower cells 

 of the stalk. Mucilage hairs, which arise from the apical cell through 

 a segment being cut off obliquely, are present in some species 

 though they may disappear with age. The axis and main branches 

 form a solid frond due to cortication which commences near the 



