62 A TEXTBOOK OF THEORETICAL BOTANY 



whole coenobium is embedded in mucilage which possesses a firm boundary 

 layer. The peripheral cells are inclined at an angle to the vertical axis of the 

 plate, and each possesses a pair of long equal flagella which are directed 

 towards the convex surface. When in motion the whole plate spms round 

 on its axis and moves w^ith the convex surface forwards. 



Reproduction 



Gotiium reproduces both asexually and sexually (Figs. 37 and 38). 



Fig. 37. — Gomum lacustre. Stages in asexual reproduction. A, Four-celled colony. 

 B, The same in side view. C, Beginning of sub-di\ision of the cells of the colony. 



D, Cell division more advanced, one group of daughter cells already flagellated. 



E, Sub-division of cells complete. Two daughter colonies readv for liberation. {After 

 West.) 



In asexual reproduction all the sixteen cells of the colony divide simul- 

 taneously, each forming a daughter colony of sixteen cells. The divisions 

 of each cell are all longitudinal. If a cell of a Goniiim colony be artificially 

 detached it at once divides up so as to form a new colony of normal size. 



Sexual reproduction is by means of naked isogametes which are 

 produced in sexual coenobia of small size. The gametes are liberated from 

 the coenobium by the breakdown of the surrounding membrane. Gametes 

 from the same colony do not fuse together, in fact there appears to be a 



