io6 



THE ALGAE 



sheath of pectose. Any cell is capable of division, and vegetative 



reproduction by fragmentation is exceedingly common, three 



methods having been described : 



(a) The septum between two cells spUts and a mucilaginous 



jelly develops in between, so that when one cell subsequently 



develops a high turgor pressure the cells become forced 



apart. 



^ 



1 



I H G F 



Ti»S'7> 



B 



Fig. 59 Spirogyra. A, B, cell disjunction (diagrammatic). C-E, cell 

 disjunction in 5. coUigata. F-H, S. weberi, cell disjunction by 

 replicate fragmentation, r = replication of septum. I, vegetative 

 structure and cell division, 5. nitida ( x 266). J, K, cell disjunction 

 and development of replicate septa. (A-H, J, K, after Fritsch; I, 



after Scott.) 



(b) Ring-like projections develop on both sides of a septum and 

 the middle lamella dissolves. Then the rings of one cell 

 evaginate and force the cells apart whilst the rings of the 

 other cell evaginate after separation {replicate fragmentation) 

 (cf. Fig. 59, F-H). 



