CHYTRIDIALES 23 



3. OoMYCETES. Sexual reproduction accomplished by the fer- 

 tilization of an egg-cell by an antherid. 



4. Saprolegniales. (Mostly aquatic moulds.) 



5. Peronosporales. (Parasites on spermaphytes.) 



The orders may be more easily distinguished by the following 

 somewhat artificial key, based on more easily noted characters : 



Mycelium wanting or poorly developed ; sexual reproduction usually 

 wanting ; parasites on algae, protozoans or rarely on spermaphytes. 



CHYTRIDIALES. 



Mycelium well developed. 



Asexual reproduction by zoospores; aquatic moulds (one species par- 

 asitic on seedlings). SAPROLEGNIALES. 



Asexual reproduction by aerial conidia or sporangia. 



Parasitic on spermaphytes. Peronosporales. 



Parasitic on insects. Entomophthorales. 



Saprophytic moulds or parasitic on other moulds. Mucorales. 



Order i. CHYTRIDIALES. 



The Chytridiales are parasitic plants of low organization often 

 confined to a single cell. They prey for the greater part on in- 

 fusoria and other protozoans, desmids, diatoms {cf. PL 2,/. /), 

 filamentous algae and other fungi. A few live in pollen grains, 

 and others, notably members of the genus Synchytriiini, are para- 

 sitic in the foliage of the higher plants. 



The species of Synchytrium have no myceliuln, the plant body 

 consisting of a single cell living parasitic either in a single epider- 

 mal cell of its host which it greatly enlarges into a gall {PI. 2, f. 2), 

 or forming a gall from a number of cells (/*/. 2, f. /). The para- 

 site either becomes a resting spore or a sporangium. In either case 

 reproduction is accomplished by the formation of zoospores. A 

 common species is S. decipiens which is found on the leaves of 

 Falcata during the entire season, and bears a superficial resem- 

 blance to a red rust {Uredo) in which genus in fact, it was 

 originally described. An allied species is found on Oenothera. 

 One of the species parasitic in a single cell is found on Aiteinone 

 in early spring, forming little reddish papilliform galls on the 

 upper surfaces of the leaf. 



Certain of the members of this order do not form a cell wall 

 even, while some develop a sort of imperfect mycelium. In 



