106 PHYCOMYCETES. 



A. Lower Fungi (Phtcomtcetes).' 



The lower fungi possess, at least in their earlier stages, 

 single-celled mycelia, which may in the higher families become 

 branched. They reproduce sexually by oospores or zygospores, 

 asexually by conidia. The Phycomycetes are divided into : 

 Chytridiaceae, Zygomycetes, and Oomycetes. 



(1) CHYTRIDIACEAE. 



The fungi of this family are chiefly parasites on aquatic 

 plants, or on land-plants inhabiting moist places. The my- 

 celium is one-celled, very rudimentary, or altogether absent. 

 Asexual reproduction takes place by the formation of zoo- 

 sporangia which usually produce uniciliate swarm-spores. Sexual 

 reproduction is rare, and is effected by fructification of one 

 cell by a fertilization-tube from another ; the resulting bodies 

 are zoosporangia which on germination set free swarm-spores. 

 Hibernation is effected by resting-spores produced from sporangia 

 in which the formation of swarm-spores is suppressed, and 

 which become clothed in a thick membrane. Some of the 

 species cause interesting deformations on the organs of plants. 



The Chytridiaceae include the families of Olpidiaceae, Synchy- 

 triaceae, Cladochytriaceae, Bhizidiaceae, Hypochytriaceae, and Oochy- 

 triaceae. Of these, only the first three contain species parasitic 

 on higher plants. They occur epidemic only in moist situations, 

 and rarely cause great damage to cultivated plants. 



OLPIDIACEAE. 



The whole vegetative body becomes a single zoosporangium 

 or a resting-spore. Sexual reproduction is very rare. 



Olpidium. 



The vegetative body consists of a naked mass of protoplasm, 

 the product of a single spore. This becomes later enveloped 

 in a thin wall of cellulose, and forms a zoosporangium with a 

 long neck through which the cell-contents are ejected as 

 uniciliate swarm-spores. The cellulose membrane may become 

 thicker and a resting-spore (sporangium) result, which in course 

 of time germinates and gives off swarm-spores. 



' Bibliography— A. Fischer in Rabeuhorst's Kryptogamen Flora, 1892. 

 Sohroeter in Enghr-Prantl Pfianzenfamilien, 1892. 



