Fungi. 207 



abate ; their cilia disappear, the spore becomes immovable and takes a 

 globular form and becomes covered with a cellulose membrane. ' ' After- 

 wards the spore emits from any point whatever of its surface a thin, 

 straight or flexuous tube, which attains a length of from two to ten times 

 the diameter of the spore. The protoplasm enters this tube and on 

 growing plants the tube forces its way into a stoma, or pore, of the leaf 

 of its victim, and spreads its branches, forming the mycelium in the 

 intercellular passages. These oogonia are matured on dried leaves during 

 winter, which kills the rest of the plant. 



By some, the Peronospora the potato fungus is thought to be 

 related to this Cystopus, although it is generally classed with the Muce- 

 dines. It has the two modes of reproduction, by summer, Conidia, and 

 the winter Oogonia, the same as described above. There are some 

 other genera in which this mode prevails. Among the Physomycetes 

 and Ascomycetes, fifth and sixth families above, there are also two 

 modes of reproduction ; one by the sporangia, and the other by the 

 conjugation of two stems and the resulting development of zygospores 

 literally "yoke-spores." The process, in the case of Mucor phycomy- 

 ces, is thus described. Two slender threads lean up against each other 

 and are in close contact for a considerable part of their length, the sur- 

 face of contact becoming uneven by parts of each protruding into the 

 other. Then the two ends arch back and over towards each other, the 

 tips touching. These then enlarge and unite into a single globular 

 spore, finally covered with warts or prominences when ripe. 



Another of the Mucors, the Rhizopus-nigricans, produces a zygospore 

 in a manner somewhat similar. First cylindrical processes are formed 

 on two threads, which then grow toward each other and unite their ends, 

 which become cemented into one mass which swells into an ovoid body. 

 A stricture is formed on each side of the swelling which, growing 

 deeper by the time the zygospore is mature, cuts it off and drops it. 



The sexual impregnation that takes place in the species of the Sapro- 

 Irgniei, one of the orders of the Physomycetes, is also very remarkable. 

 An oogonium is first formed on top of a short stem which grows from 

 the mycelium, and it appears to be the receptacle of female cells, a sort 

 of uterus, in fact. Now, below the oogonium and from the stem on 

 which it is perched, a tube is developed, which, growing out of the stem, 

 curves upward and back toward the oogonium, until its end touches it 

 and penetrates its shell. Protoplasm then passes into the oogonium 

 from the tube, accompanied with granulations and some very lively 

 corpuscles, which are supposed, with probability, to be spermatozooids. 

 The male tube is called an antheridium, it evidently answering the same 

 end as the anther of flowering plants. It occurs in some form in a 

 great many species besides those named here. 



