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 zoogomdia. Hach 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. 
Fie. 167.—Ascr. fren Peziza, 
a, b, ¢, d, e, f, stages in 
Fic. 166.—Ca@ynocytr or Muc.r, BEARING A development. In f the 
Gonipaneium, &, THIS 18 MORE HIGHLY ascospores are mature. The 
MAGNIFIED IN THE FIGURE TO THE RIGHT. slender cells are barren 
ee hairs, or paraphyses, X 
m, columella; 7, gonidia. 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 
