ObPBTTA. 131 



chlorophyll-bearing, but a few are colorless saprophytes 

 and parasites. 



272. Four classes have been distinguished: 



1. ZodsporecB, analogous and related to the ZoOsporese of Branch II. 



3. CEdogoniem; plant-body a cellular filament. 



3. CahUaatem ; plant-body a tubular filament. 



4. Vueacem; plant-body large and complex; color olive-green. 



Class I. Zoospores. 



273. The little spherical Volvox of the pools and ditches 

 may be taken as an illustration of the first class. It resem- 

 bles Pandorina in many respects, 

 and without doubt is cloSely re- 

 lated to it. Volvox is a colony of 

 very many little cells, each of 

 which projects its two cilia out- 

 ward, giving the ball a hairy ap- 

 pearance. By the lashing of the 

 cilia the ball rolls about in the 



■water. Ficf. eo.— a Volvox colony, 



nt, , kj. J. • i. £ magnified about 45 times, 



274. At a Certam stage some or showing young colonies with- 



the cells enlarge and slip into the 



interior of the colony, becoming free oogones, each con- 

 taining one germ-cell. At the same time other cells break 

 up their protoplasm into motile antherozoids, which escape 

 into the same cavity of the colony. At length the anthero- 

 zoids unite with the germ-cell, when as a result the latter 

 secretes a thick wall, and thus becomes a resting spore. 

 Upon germination the resting spore divides its protoplasm 

 into several hundred small cells, which then arrange them- 

 selves into a new colony. 



275. The asexual reproduction takes place by certain 

 Cells breaking into great numbers of little cells, which then 



