ANNUAL WINTER MEETING AT WARRENSBURG. 241 



give rise to a second crop of conidia ; this process continues until frost, 

 when the resting spores are formed. 



The order Perono spore Ltd to which this fungus belongs contains 

 some very destructive species. Peronospora infestans is the potato 

 fungus which occurs in the leaves, stems and tubers of the potato. 



P. ViciiV, forms a white coating on the leaves of the garden pea^ 

 The reproduction and growth of all the above species agree with the 

 one on grape leaves. 



The next group of fungi to which we invite your attention is 

 known to botanists as the order Eysiphacece. The members of this 

 order usually occur late in the summer, and they cover the leaves of 

 the plants they attack with a dirty white coating. 



Unlike the members of the preceding order the vegetative por- 

 tion of these parasites is superficial, that it is on the exterior of the 

 leaf. One of the best known species as well as the most interesting to 

 you as horticulturists, is that which occurs on the leaves of the grape 

 and commonly known as ttie European grape mildew to distinguish 

 it from the American species already described. 



This fungus is known to botanists as Uncinula spirallis^ and it is 

 believed that this species and one that occurs on the vines in Europe 

 are identical. At any rate as far as the life history of both have been 

 traced there is no difference between them. As stated above, the 

 plant body, which resembles a dense mass of cobwebs is on the exterior 

 of the leaf, and nourishment is obtained by means of irregular pro- 

 tuberances which project from the side of the mycelium, next the leaf. 

 It is believed by some that these projections penetrate the walls 

 of the cells next to the epidermis of the leaf, using the contents of 

 these cells in the building up of their own body. 



These parasites are propagated during the summer months in the 

 following manner: The cobweblike threads on the exterior of the 

 leaf send up a number of short branches; these branches are cylin- 

 drical and at first one celled, but ultimately there are several trans- 

 verse partitions formed across the upper end of the branch, dividing it 

 into several cells. When these cells have attained the proper size they 

 separate from the stalks supporting them and constitute what is 

 known as the conidia^ or summer spores. 



The conidia are blown about by the wind, and when they fall upon 

 the proper host plant and there is sufficient moisture and heat pres- 

 ent, they germinate and ultimately give rise to the white cobweb- 

 like thread from which they originated. 



Late in the fall if we examine a leaf of any plant infected with 

 one of these parasites, we will find scattered among the white cobweb- 

 H R— 16 



