2 8 Minnesota Plant Diseases. 



and fruits — their radius of distribution is proportionately in- 

 creased by increase of height from ground. Rust spores can 

 be blown for great distances and still retain their power to in- 

 fect plants. In this connection one sees in the structure of 

 these spores a certain adaptation which assists in the wind 

 sowing. The food material packed up in the spore is usually 

 oily and is therefore light in weight. The spore-coat, more- 

 over, has often spiny projections which enable the spore to ad- 

 here to objects with which it comes in contact. Moreover, 

 the summer spores of rusts are often formed continuously for 

 a long period, — throughout the summer, — that is to say, the 

 fungus scatters its chances over a long period rather than con- 

 centrate the production into one eftort. The mildews are like- 

 wise parasites with a similar habit of spore distribution. The 

 mushrooms and their allies have learned to use the wind in 

 sowing their spores. The stalked, unbrella-like, fruiting body 

 raises the spores into the air and at maturity sheds them where 

 the wind can take them up. Many shelf fungi on the trunks 

 of trees have acquired especially elevated positions. Such 

 fungi can be said to concentrate their efforts upon the produc- 

 tion of an enormous number of spores for distribution in a 

 comparatively short time and a favorable period is of course 

 sought for this effort. The spores of mushrooms are in gen- 

 eral smooth-coated, as they usually come to the ground before 

 they germinate and require no special means of attachment. 

 Puff-balls also form myriads of spores but do not shed them 

 all at once or in such a short time. Gusts of winds, or a jar by 

 some falling object, may force out little clouds or puffs of 

 spores and such a puffing goes on intermittently for a long 

 period. 



Distribution by insects. Again some fungi have learned to 

 use insects as an aid in spore distribution. A very effective de- 

 vice has been invented by the fungus which forms ergot of rye. 

 Previous to the formation of the storage organ known as the 

 ergot, the fungus forms a soft mass of much branched threads 

 in the young grain and from these are formed summer spores. 

 These are accompanied by an attractive sugary solution which 

 is luring to insects and with this sugar food the latter carry 

 off the spores, sowing them on other flowers and thus rapidly 



