CONJUGALES 



99 



whilst others maintain that there is only an inner cellulose layer 

 with an outer cuticle. The whole filament is enclosed in a mucilage 

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



u 



I H G F 



B 



Fig. 67. Spirogyra. A, B, cell disjunction (diagrammatic). C-E, cell dis- 

 junction in S. colligata. F-H, S. Weberi, cell disjunction by replicate fragmenta- 

 tion, r = replication of septum. I, vegetative structure and cell division, 

 S. nitida ( x 266). J, K, cell disjunction and development of replicate septa. 

 (A-H, J, K, after Fritsch; I, after Scott.) 



reproduction by fragmentation is exceedingly common, three 

 methods having been described : 



{a) The septum between two cells splits and a mucilaginous 

 jelly develops in between, so that when one cell subsequently de- 

 velops a high turgor pressure the cells become forced apart. 



{h) Ring-like projections develop on both sides of a septum and 

 the middle lamella dissolves. Then the rings of one cell evaginate 



7-2 



