I50 



Minnesota Plant Diseases. 



count of the infrequency of the occurrence of proper condi- 

 tions, it might forget how to form sac-spores and would thus 

 become independent of the sac-spore form. Both the produc- 

 tion of different kinds of spores by one fungus plant and the 

 production of spores on different hosts in one life-cycle would 

 tend to furnish fungi where such a separation might occur. In 

 addition to those forms where this actual separation and inde- 

 pendence occurs there is a considerable assembly of spores, 



where the connection 

 of apparently inde- 

 pendent forms with 

 sac-spore stages is 

 known, and in such 

 cases the term "imper- 

 fect" is in a sense a 

 misnomer. In a vast 

 number of forms, the 

 connection is indicated 

 to a certain degree by 

 the connections of an- 

 alogous forms. For 

 instance, the accessory 

 spore forms of the 

 powdery mildew is of a 

 definite type known as 

 an Oidium, and when 

 one meets with such 

 isolated spore forms, if 

 they occur in the usual 

 habitats of mildews, one may refer them to the powdery mil- 

 dew group. Indeed it may be that all so-called imperfect 

 fungi are actually traceable in their connections with sac-spore 

 forms, but many have, as yet, frustrated all attempts to prove 

 such connections. We may sum up these forms in this re- 

 spect into three groups : first, those isolated forms whose con- 

 nection with sac-spore forms is known; second, those isolated 

 forms whose sac-spore connection is not known, but suspected 

 from analogy with known forms; third, those isolated forms 

 whose sac-spore connections are not even suspected or have 

 become actually independent. 



Fic. 69.— Truffle. 1. Fruiting body cut open; surface 

 furrow which corresponds to the opening of a 

 cup fungus is seen below and the convoluted sur- 

 faces of the cup interior above. 2. A portion of 

 the interior showing the sacs, each with four 

 spores (highly magnified). 3. A single sac show- 

 ing four spiny spores. Very highly magnified. 

 After F. K. Butters. 



