334 



FUNGI 



Pringsheim). These resting cells or sporanges are formed only on 



old myceles, and by no means regularly. 



The zoosporanges vary in form with the 

 genus, and in a minor degree with the 

 species. The usual form is a large club- 

 shaped zoosporange containing a great 

 number of biciliated zoospores, which 

 escape from it through an opening at the 

 apex ; though in poorly developed indi- 

 viduals (and normally in Aphanomyces, de 

 By.), the zoosporange is more cylindrical, 

 and only one row of zoospores is formed. 

 In Saprolegnia (Nees ab Esenb.) the zoo- 

 spores are actively motile when they escape. 

 Their activity ceases for the most part 

 after a few minutes ; they settle down, 

 assume a thin cellulose-membrane, rest 

 for a short time, only to escape from this 

 membrane, and resume active movement 

 before final settling down and germina- 

 tion. The spores of individuals may on 

 the other hand omit the second period of 

 movement, and germinate directly on first 

 settling down. In Achlya (Nees ab Esenb.) 

 and Aphanomyces the spores escape from 

 the sporange without cilia and active 

 movement. They arrange themselves in 

 globular fashion outside the apex of the 

 sporange, assume each a thin cellulose- 

 membrane, within which they rest for a 

 few hours, and, escaping from it, swim 

 about, and, settling down, ultimately ger- 

 minate. In the sporanges of Dictyuchus 

 (Leitg.) the spores are each enclosed in 



net-like cellulose walls, from which they escape, not by any special 



orifice of the sporange, but by taking as it were the shortest cut through 



the sporangial wall and empty spore -cases if they come in the way. 



In Aplanes Braunii (de By.) the formation of propagating spores is 



as a rule omitted. When produced they give rise to germ-tubes directly 



without swarming. 



The zoospores produced by oosperms behave, so far as is known 



like those from the corresponding zoosporanges. 



FIG. 292. Zoosporanges of Achlya 

 N. ab E. A , with zoospores formed 

 but still enclosed. , with zoo- 

 spores escaping. At a they are in- 

 vested with a cell-membrane, at c 

 they are free, empty membranes 

 at b (x about 300). (After de Bary.) 



