Minnesota Plant Diseases. 



149 



consists of a great labyrinth of pockets and canals which are 

 lined with the spore sacs. The truffles which have been found 

 up to the present time in Minnesota are not large, the largest 

 reaching the size of 

 a small walnut. 

 They are brownish 

 or blackish in color 

 and regularly or ir- 

 regularly spherical 

 in shape. Two 

 forms have been 

 discovered and un- 

 doubtedly more ex- 

 ist. Many forms 

 mature their under- 

 ground cups late in 

 autumn so that 

 they can be found in 

 the ground in early 

 spring. Others ma- 

 ture in the summer. 

 (Figs. 10, 68, 69.) 



Imperfect fungi 

 and leaf spots {Fungi 

 imperfecti). As has 

 already been ex- 

 plained, the so- 

 called imperfect 

 fungi include an 

 enormous number 

 of plants which are 

 as yet incompletely 

 known. Most of 

 them are undoubt- 

 edly accessory spore-forms of the black fungi or of the cup fungi. 

 One can imagine that a fungus spore-form of this kind might be- 

 come separated from its connection in the life-story of a 

 black fungus, in that the mycelium arising from such a spore 

 would give rise only to the accessory spore-form. On ac- 





Fig. 68.— Truffles (Tuber lyoni). The truffle may be re- 

 garded as an unopened cup fungus with its internal 

 spore-bearing surface greatly convoluted. That which 

 corresponds to the opening of the cup fungus is seen 

 as a furrow m 2 and in the sections 1 as a broad 

 whitish streak. 1 shows the truffle cut open; the 

 chambers in which the spore-sacs are formed can be 

 clearly seen. Photograph by F. K. Butters. 



