Minnesota Plant Diseases, 



33 



mass of the latter breaks away and is shot off with considera- 

 ble force. One of the most interesting devices is that found 

 in the ball-throwing fungus. This is a very tiny puff-ball, little 

 larger than a pin head. The spores are not released in a pow- 

 der as is usual in the puff-balls, but cling together in a ball-like 

 mass. The outer coats of the puff-ball burst open in star- 

 shaped fashion and the inner coats suddenly invert, throwing 

 the ball a yard or more into the air, reminding one of the simi- 

 lar methods which certain seed plants, as the common touch- 

 me-not, utilize to cast their seeds abroad. 



Spore resistance. Just as one finds great diversity in the 

 form and method of production of fungus spores, so also may 

 one find great differences in their powers of resistance. The 

 presence of moisture is often a crucial factor in determining 

 the life of a spore. The spores of many of the algal-fungi, 

 most of which are aquatic in habit, cannot endure a dry atmos- 

 phere for any considerable length of time. This is particularly 

 true of the- swimming spores, which are peculiarly adapted to 

 the water habit. When such spores are dried they lose their 

 powder of germination they are dead. The great majority of 

 fungus spores can, however, endure desiccation with perfect 

 impunity. Such spores as smut spores have been known to 

 retain their vitality for eight years or more in an air-dried con- 

 dition. The spores of the ordinary green molds are also capa- 

 ble of living in dry atmospheres for a very long time. That the 

 atmosphere of an ordinary room contains many such spores in 

 full vigor of life can readily be demonstrated by exposing nutri- 

 ent gelatine to the air, when colonies of green or blue molds 

 will be produced in a few clays. Such spores are always, after 

 their maturity, ready for germination. 



Moreover, the air-dried spores of fungi are in general capa- 

 ble of resisting high and low temperatures, much more so than 

 spores in moist conditions. Blue mold spores can survive dry 

 temperatures of several degrees above the boiling point of wa- 

 ter. But under moist conditions they never survive this tem- 

 perature ; in fact, they succumb at temperatures considerably 

 below it. The common treatment for smuts is based on this 

 fact, for smut spores perish in water considerably below boiling 

 water temperature. On the other hand, dry spores can endure 



