120 Minnesota Plant Diseases. 



the custom now obtains in some breweries of using only pure 

 cultures of yeasts of a known kind, thus insuring uniform re- 

 sults. Certain wild yeasts and bacteria may find their way 

 into the brew and by the formation of peculiar compounds may 

 spoil the flavor. It has already been mentioned that certain 

 yeast-like fungi cause several diseases of lower animals as well 

 as thrush and sore throat in children. The systematic position 

 of these fungi, however, is uncertain at present since the sac- 

 spores have not been found. The power of fermentation is not 

 confined exclusively to the yeasts since other fungi, though not 

 many, possess this power, and it is possible that the thrush fun- 

 gus is a member of some other group of fungi. As far as is 

 known at present no yeasts can be said to cause undoubted 

 parasitic disease in plants. It must be remembered, however, 

 that in the exuding sugary juices of fruit under natural condi- 

 tions, or from wounds, yeast cells are very commonly found, 

 and it is not inconceivable that they work their way into the 

 fruit and assist in fruit rot. (Fig. 48.) 



Slime-flux fungi (Endomycetacea). In the slimy exudations 

 which often flow from wounds in trees a great variety of such 

 organisms as bacteria and fungi abound, and among them a 

 close relative of the yeast fungi is not uncommon. This fun- 

 gus differs from the yeasts in always possessing a thread myce- 

 lium and forms its spores on branches of this mycelium. It is 

 not certain whether or not this fungus is the cause of the flux 

 or whether it simply finds in the flux congenial conditions and 

 appropriate food. 



Leaf curls and plum pockets (Exoascacea). These fungi 

 are of frequent occurrence on plants of the plum family such as 

 domestic plums and cherries and peach plants. The host plant 

 part is usually swollen. Leaves thus affected sometimes curl 

 much and become distorted. Plum and cherry fruits when at- 

 tacked by the fungus form the well-known "pockets" without 

 stones. Both pockets and curls bear the spores of the fungus 

 in a layer which covers the whole or a considerable part of the 

 affected organ. This region takes on a greyish white color 

 which is due to the presence of a great number of short cylin- 

 drical sacs, each containing eight spores. The spore-sacs stand 

 side by side, like posts in a palisade, upon the surface of the 



