THE MICROSCOPE IN HISTOLOGY AND BOTANY. 137 



material in a state of decay, which is more or less com- 

 plete. The prevalence of atmospheric changes, variations 

 in light, heat, moisture, and electricity, etc., have much 

 to do in predisposing vegetable as well as animal tissues to 

 disease and producing epidemics. The agriculturist, there- 

 fore, as well as the physician, must discriminate between 

 those diseased conditions which provide a habitat for 

 fungi, and the effects produced by the fungi themselves. 



Impregnating wood with corrosive sublimate or chlo- 

 ride of zinc has been used to prevent dry rot in wood, and 

 soaking seeds in alkaline solutions or sulphate of copper 

 is said to remove smut and similar fungus spores. 



The development of fungi is from spores or conidia. 

 Plate IX, Fig. 107, represents the Torula vegetating by 

 the budding of its spores. These buds rapidly fall off and 

 become independent cells. In other varieties self-division 

 gives rise to the mycelium, a mass of fibres often inter- 

 laced so as to form a sort of felt. Some branches of this 

 mycelium (hyphce) hang down, while others rise above the 

 surface (conidiophores) and bear conidia, which fall off and 

 develop into new hyphee (Plate IX, Fig. 108). In the 

 "blight" of the potato the mycelium is loose, and the 

 hyphae ramify in the intercellular spaces and give off pro- 

 jections into the cells of the plant. The conidia germinate 

 by bursting the sac which contains them, putting forth 

 cilia, moving awhile, then resting and enveloping them- 

 selves with membrane and growing into hyphse. In the 

 autumn, parts of the hyphae assume special functions. 

 One part develops a spherical mass called oogonium, while 

 another becomes a smaller mass or antheridium. When 

 the first is ripe, it is penetrated by the latter, and the 

 bioplasms of each are fused together. The antheridium 

 then decays, while the oogonium grows and becomes au 

 oospore, in which the bioplasm divides and subdivides. 

 Next season each segment escapes ciliated, and moves 

 about till it finds a place to germinate. In Achyla two 



