B 



42 THE ALGAE 



eventually settles on the leaf of a host plant and secretes a wall. 



Tubular prolongations grow out from these bodies and enter the 



host, either by way of the stomata 

 or else between two epidermal 

 cells. Subsequently the end of 

 the tube swells out into an eUip- 

 soidal or lobed structure into 

 which the contents of the s warmer 

 pass. In Chlorochytrium lemnae^ 

 which attacks duckweed {Lemna\ 

 the endoparasitic cells sink down 

 in the old Lemna fronds to the 

 bottom of the pond or stream 

 and remain dormant until the 

 next spring. There is evidence 

 that reduction division takes 

 place at gamete formation so 

 that the vegetative phase must be 

 diploid. 



Plants of the aUied genus Rhod- 

 ochytrium are colourless and hence 



it has been suggested that the simple fungi {Chytridiales) may have 



been derived from these algae. 



Fig. 17. Chlorochytrium lemnae. A, 



entrance of zygote into host. B, resting 



cells in leaf of Lemna. C, resting cell. 



(After Fritsch.) 



Chlorellaceae: Chlorella {chlor, green; ella, diminutive of affec- 

 tion). Fig. 18 

 The globular cells are non-motile, solitary or aggregated into 



E D 



ABC 



Fig. 18 Chlorella vulgaris. A, single cell. B, division into four. C, 



final stage of division into four daughter cells. D, first stage of 



division into eight. E, F, second and third stages of division into 



eight daughter cells. (After Grintzesco.) 



