CLASSIFICATION OF FUNGI 35 



live on living or dead insects, pin-worms, fishes, etc. 

 They consist of branching mycelium which force their 

 way through the body wall, ramify throughout the body 

 of the host, and eventually come to the surface where 

 they produce masses of long cotton-like mycelia. Some 

 of these hyphae form long tubular sporangia in which 

 are produced, by internal division, great numbers of zoo- 

 spores (Fig. 13). These zoospores are very active, swim 

 rapidly for a short time and attach themselves to some 

 dead or wounded animal, penetrate the body and pro- 

 duce a new growth. In the sexual reproduction an 

 oogonium or female organ containing a few egg cells, 

 and an antheridium or male organ are formed ; the 

 antheridium penetrates the oogonium, but so far as 

 known, its contents do not unite with the egg cells. 

 However, the egg cells rest for a time, and then under 

 favourable conditions break up into a number of zoo- 

 spores which behave the same as the zoospores from the 

 sporangia. These fungi are the source of great annoy- 

 ance in the fish hatcheries where they sometimes kill 

 great numbers of young fish. 



Certain other species of the genus Pythium 1 (Fig. 22) 

 of this order, are saprophytic on the decaying organic 

 materials in wet soils and manures, but when opportunity 

 offers make parasitic attacks on seedling plants, causing 

 the well known "damping off" disease (pp. 29, 106, 

 221, 236). The attack is made at the surface of the 

 ground and usually results in the death of the host. 

 These young plants then undergo decay, and the fungus 

 continues to live saprophytically upon them. The cork 

 and cuticle covering of these young plants is so thin 

 that they cannot withstand the attack of the fungus, 

 but if protected in their early growth, they very soon 

 become strong enough to resist the disease. These are 

 among the most troublesome and destructive seed-bed 

 diseases. The members of the mustard family are especi- 

 ally susceptible, and in tropical countries tobacco, cotton, 



1 Certain characters indicate that Pythium may be intermediate between 

 Saprolegniales and Pronosporales. 



