Minnesota Plant Diseases. 395 



The spores are formed usually in fours, inside of small sacs, 

 which are formed on the ends of branches of the mycelium. 

 These little sacs or asci are not enclosed in any special covering 

 but are free upon the mycelium. 



The red disease of mushroonis [Hypomyces lactiHuorum 

 (Schw.) Tul.]. This is a conspicuous though not very abundant 

 disease of wild mushrooms. It is usually found on the milk 

 mushrooms. The disease-fungus is a member of the burnt- 

 wood fungi, though it has not the black color of most of these 

 plants. An attacked milk mushroom becomes greatly modified 

 in structure. It does not form gills as under normal conditions 

 but the entire surface of the mushroom is smooth. It is there- 

 fore roughly top-shaped with the peg in the ground. The sur- 

 face is colored a very brilliant red (scarlet to orange red), which 

 makes the diseased plant a very conspicuous object in the 

 woods. This color is imparted to it by the parasitic fungus. 

 All over the surface one sees the slightly protruding tips of the 

 sac-spore-capsules which are spherical to pear-shaped and are 

 partially embedded in the tissues of the host. Through an 

 apical opening the sac spores escape in enormous numbers so 

 that if the diseased mushroom be placed under a bell jar for 

 several hours, and left undisturbed, a dense white powder of sac 

 spores from the parasite will fall on the underlying glass. 

 These spores are presumably again capable of causing infection. 



Powdery mildew of hazel [Phyllactinia suffulta (Reb.) 

 Sacc.]. Hazels are very cornmonly attacked by a blight, which 

 occurs also on many other trees, such as birch, oak and ash, 

 though not so abundantly on these. A fine, white, cobwebby 

 mycelium is formed on the leaves, upon which the sac-capsules 

 arise in the fall. The sac-capsules are readily recognized among 

 the powdery mildews by the peculiar appendages which are 

 colorless and straight, and when mature have a swollen bulb 

 at the point of attachment to the capsule. The appendages are 

 not very numerous. The capsules contain a number of sacs, 

 each of which encloses eight spores. Although the disease is 

 very common, the damage done is usually slight and does not 

 call for combative measures. 



Powdery mildew of vetch and crowfoot [Erysiphe com- 

 munis (Wall.) Fr.]. This blight is an exceedingly common para- 



