288 



PART IV. VEGETABLE TAXONOMY. 



related one, the small cells produced by the division of the 

 parent cell, have been observed to conjugate. 



b c d 



Fig. 483. — Euglena viridis. a, a, motile forms, each provided with a long flagellum 

 and an "eye-spot ; b, one of the cells passing into the encysted stage ; c, encysted form; 

 d, encysted form discharging minute swarm-spores. 



Pandorina and Volvox may be taken to illustrate the forms which 

 produce ccenobia. In Pandorina the coenobia consist of sixteen, 

 or less commonly of eight or thirty-two cells, crowded into a 

 spheroidal mass, and surrounded by a transparent gelatinous 

 envelope. Each cell possesses two cilia which project through 

 the envelope and by which the colony is propelled with ?. rolling 

 motion through the water. Asexual reproduction takes place 



Fig. 484. — Pandorina Morum, a fresh-water alga, a, colony of sixteen cells, each pro- 

 vided with a pair of cilia, by means of which the whole colony moves through the water 

 with a rolling motion; b, two zoospores of the same plant in the act of conjugation; c, the 

 process nearly completed. Magnified about 150 diameters. 



by the formation of sixteen new cells in the interior of each cell 

 of the colony. These young colonies after a time escape from 

 the parent cells and form independent coenobia. 



In the sexual reproduction, cell-division takes place as before, 

 but the cells which are formed escape from their enclosure by 



