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'e 

 spore-sac capsule. 

 The powdery mil- 

 dews live entirely on 

 the outside of leaves 

 and young branches 

 of plants and are 

 often dangerous 

 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 

 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-dew fungi (Pyrenomycetinecz 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 



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. 



