Minnesota Plant Diseases. 



2 5 



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 walls. 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- 



FIG. 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. 



