74 



Minnesota Plant Life. 



through the activity of different organisms. The peculiarity of 

 the yeast plant is its capacity for setting up alcoholic fermenta- 

 tion and no other kind. 



Besides the common yeasts a number of others exist. One 

 kind which grows in cabbage, after it is cooked, produces the 

 substances which give the flavor of sauerkraut. Another kind 

 when introduced into milk causes it to ferment, and in the re- 

 gion of the Caucasus is used by the Tartars to change goat's or 

 camel's milk into an intoxicating liquor. 



Plum-pockets. Very 

 closely related to the yeasts 

 is a group of parasitic fungi 

 capable of attacking a va- 

 riety of plant-tissues. One 

 kind, when it infects the 

 young fruits of the plum or 

 cherry produces what is 

 known as plum-pocket. 

 When such a fungus grows 

 upon a plum it distorts it 

 and gives it a singular, ir- 

 regular baggy appearance 

 which is easily recognized. 

 The poplar trees in Minne- 

 sota are very often attacked 

 by a pocket-fungus, which 

 changes their green pods 

 into yellow sacs distinctly 

 larger than the ordinary 

 pod. On cherry trees, a 

 witch's broom formation in 

 which the growth of the 

 twigs is disordered, results from the presence of a fungus of this 

 group, and upon alders another witch's broom arises under sim- 

 ilar conditions. 



Morels. In the sac-fungi which have been described no 

 conspicuous special body is developed ; but in the higher forms 

 large bodies, rivalling the mushrooms in size, and of a great 

 variety of form and structure may be produced. Of such, one 



FIG. 25. Pocket-fungus on sand-cherry. After 

 Bailey. Bull. 70, Cornell Ag. Kxp. Station. 



