Minnesota Plant Diseases. 



25 



forcibly eject their spores. Often by a change in the atmos- 

 pheric conditions a large number of sacs burst at once and 

 clouds of spores can be seen to ascend from the cup. The truf- 

 fles have underground closed fruiting bodies which are related 

 to the cups but never open except by decay of the w^alls. The 

 morels and their allies have cups which are turned inside out, 

 as it were, and are furthermore usually much wrinkled, and 

 borne on stalks.~ Another very important phase of reproduc- 

 tion in fungi lies in the kinds of spores produced by a given 

 fungus. One and the same fungus may often produce more 

 than one kind of spore. In fact, some fungi produce as many 



as five or six kinds. 

 The wheat-rust, for 

 example, forms one or 

 more, — commonly 

 two, — kinds of spores 

 in the spring, another 

 in summer and anoth- 

 er in the autumn and 

 when the autumn 

 spores grow in early 

 spring still another 

 kind is produced. 

 These spore forms fol- 

 low in a certain way 

 the seasons. The mil- 

 dew, for instance, has 

 summer spores and 

 winter spores. In oth- 

 er fungi the various 

 forms may be called 

 forth by differences in the substances upon which the fungus 

 grows. In some fish-molds the production of the different 

 spores can be exactly controlled by changing the food sub- 

 stances. Sometimes a fungus which is or has been capable of 

 producing several spore-forms continues under certain condi- 

 tions to produce only one kind of spore. Our knowledge of 

 such a fungus is incomplete until we know the other spore- 

 forms which it is capable of producing. There is a vast num- 



^;^ 



Fi c. 11. — Kinds of spores produced by one rust 

 fungus (a wheat rust) at different times. 1. 

 Winter spore. 2. Basidiospore. 3. Cluster-cup 

 spore. 4. Pycnidial spore (probably a function- 

 less relic of a male sexual cell). 5. Summer 

 spore. 1, 2, 4 and 5, after Ward; 3, after Ar- 

 thur and Holway. 



