PHYCOMYCETES 



259 



sporangia. Sexual reproduction by oogonia and antheria ; 

 in Saprolegnia the oogonium contains several oospores ; in 



FIG. 62. Pythium debaryanum, a parasite destructive to seedlings, 

 and causing the disease known as ' damping off.' i, seedlings of cress 

 (Lepidium) attacked by the fungus ; 2, mycelium bearing conidia at the 

 tips of the branches ; 3, sporangia in different stages, also a free zoo- 

 spore ; 4, an oosphere with the antheridium or male organ attached, which 

 has pierced the wall of the oosphere and inserted a slender tube, for the 

 purpose of allowing the contents of the antheridium to mingle with those 

 of the oosphere (after this blending of contents, or fertilisation, the 

 oosphere becomes enclosed in a newly formed cell-wall, to form the 

 oospore or sexually produced resting-spore) ; 5, a germinating conidium. 

 Fig. i, nat. size ; the remainder highly mag. 



Pythium it is monosporous. In Dictyuchus the wall of the 

 oogonium is perforated. Most of the species are truly 

 aquatic, growing on fish, insects, or aquatic plants. 



