JEndcfsphfcracece 197 



Two well-known species of Volvox exist in the deeper ponds and ditches 

 of the low-lying areas of the British Islands. They are often associated with 

 Lemna, and prefer ponds which receive a plentiful .supply of rain-water. The 

 adult colonies of V. globator Ehrenb. are 680 800 ^ in diameter, the cells are 

 very numerous, the protoplasmic strands connecting them are of considerable 

 thickness, and the ripe oospores are substellate (fig. 78 B). V. aureus Ehrenb. 

 is usually smaller than the preceding species, the adult colonies being 200 

 500 p, in diameter ; fig. 78 A, C, and D ; the cells are less numerous, the proto- 

 plasmic threads connecting them are extremely delicate, and the walls of 

 the ripe oospores are smooth. 



Family 3. ENDOSPILEJRACEJE. 



This family includes a number of endophytic Alga 3 in which 

 the plant-body is either a simple rounded cell or a slightly 

 branched coenocyte, occurring wedged between the epidermal cells 

 of aquatic or marsh-loving plants. The cells are somewhat 

 variable in form and the cell-wall is sometimes thick and lamellose, 

 often developing on one side a button-like excrescence of cellulose. 



Reproduction takes place by the formation of zoogonidia or 

 planogametes, or both. In the best known genus, Chlorochytrium 

 Cohn, the contents of the endophytic cell become broken up by 

 successive divisions, in a manner similar to that which occurs in 

 Characium, into a large number of small zoogonidia or gametes. 

 These are liberated by the gelatinization of the inner layer of the 

 cell -wall, which becomes protruded as a large vesicle such as is 

 found in the Pediastrese and many of the Protococcacese. The 

 biciliated gametes are isogamous and on their fusion the motile 

 4-ciliated zygospore comes to rest on the epidermis of the host- 

 plant. Germination takes place without any period of rest, the 

 new endophytic cell forcing a protuberance either between two 

 cells of the epidermis or into a stoma. 



Some of these endophytic cells become akinetes and in this 

 condition they pass the winter. 



There is a complete absence of ordinary vegetative division. 



Seven genera have been described, but some of these, are 

 doubtfully distinct. 



The researches of Klebs have shown that Cohn and other 

 previous investigators were wrong in regarding certain of these 

 plants as parasites, and that not merely can the endophyte live 

 quite independently of its host-plant, but that the latter receives 

 no injury beyond the little mechanical pressure exerted by the 



