Minnesota Plant Diseases. 



125 



mycelium, minute spheres about the size of a pin point. They 

 are at first white, then become yellow and finally dark brown to 

 black. They are the sac capsules and bear one or more spher- 

 ical or pear-shaped sacs with two to eight spores in each, ac- 

 cording to the species. The capsular wall has no special meth- 

 od of opening but it may often possess elaborately-shaped 

 threads known as appendages, which are often much branched 

 and form a crown 

 or circle around the 

 case. Such may as- 

 sist in the distribu- 

 tion of the who 1 e (/ *sKS 

 spore-sac capsule. 

 The powdery mil- 

 dews live entirely on 

 the outside of leaves 

 and young branches 

 of plants and are 

 often d a n g e r o u s 

 parasites. A great 

 number of our com- 

 mon garden plants 

 as well as wild flow- 

 ers are attacked by 

 some sort of pow- 

 dery mildew, though 

 the conditions are 





FIG. 51. The fruiting body of the powdery mildew of 

 black haw, showing the appendages. The sac-capsule 

 has been broken and the sacs, each with about eight 

 spores, are emerging from the split. Highly magnified. 

 Microphotograph by E. W. D. Holway. 



not usually such as 



to create epidemics. Roses and grapevines are conspicuous suf- 

 ferers as are also gooseberries and other garden plants. These 

 fungi are also found abundantly on lilac bushes, all kinds of wil- 

 lows, birches, poplars, elms, oaks, maples, and many others, but 

 on these do not often cause much damage. (Figs. 10, 50 to 52, 



134, 135, 152, 192, 202 tO 204, 210.) 



Honey-dcic fungi (Pyrcnomycctinccc in part). Structurally 

 this group of fungi is a close relative of the mildews. The 

 spore-sac-capsule is built on the same general plan but does 

 not usually contain appendages while, on the other hand, it is 

 usually furnished with a pore for the exit of the sacs and 



