428 



VEGETABLE PHYSIOLOGY 



development of such cells, conspicuous among them being 

 Saprolegnia and its allies (fig. 165). These free-swimming 

 protoplasts are known as zoospores or zoogonidia. Each on 

 coming to rest clothes itself with a cell-wall, and can develop 

 into a plant exactly like the one from which it arose. These 

 zoogonidia are developed by the protoplasm of a single cell 

 dividing up into a variable but often large number of separate 

 protoplasts, the process being known as free cell formation. 



i-fl 



FlO. 166. CffiNOCYTE OF MuC'.T, BEAB1NG A 

 GOXIDANGIUM, L THIS IS MOBE HIGHLY 

 MAGNIFIED IN THE FIGUKE TO THE BIGHT. 



m, columella ; I, gonidia. 



FIG. 167. Ascr. frcin Peziza. 

 a, b, c, d, c, f, stages in 

 development. In / the 

 ascospores arc mature. The 

 slender cells are barren 

 hairs, or paraphyses. x 

 250. 



Each protoplast possesses a nucleus derived from the original 

 nucleus of the cell in which the formation takes place, in 

 the manner already alluded to. 



In most cases where these reproductive cells are met with 

 they have not so simple a structure as those so far described, 

 but each is furnished with a cell- wall. They are commonly 

 called spores or gonidia, and arise in different ways upon 

 the plant, often, or indeed generally, being developed in or 

 on special organs, known as sporangia or gonidangia. 



The yeast-plant gives us perhaps the simplest form of 



