The Erysiphaccac of Nebraska 

 by raymond j. pool 



Introduction 



The Erysiphaceae are parasitic fungi which are popularly 

 known as " Powdery Mildews," " Blights," or " Leaf Mildew-. - ' 

 They are easily recognized by the white or colorless, more or 

 less dusty or felt-like covering on leaves, stems, or other infected 

 parts. They are common on many of our common garden and 

 field plants, as well as on many pieces of " wild " or non-cul- 

 tivated plants. The dusty appearance is due mostly to the pres- 

 ence of myriads of colorless or white conidiospores which are 

 characteristic of the " Oidium " or conidial stage in the develop- 

 ment of any given species. Later in the summer, or autumn, 

 the ascigerous form of fruit is developed which is in the shape 

 of small, more or less globular, dark brown or black perithecia. 

 The perithecia are usually provided with special outgrowths, the 

 appendages. After the perithecia are formed the mycelium 

 sometimes disappears, and the black perithecia are left on the sur- 

 face of the leaves or stems of the host ; sometimes the mycelium 

 is thick and persistent on the host and then the perithecia are 

 more or less immersed in the patches of cobwebby mycelium. 



The Erysiphaceae belong to the Ascomycetes, and they are fur- 

 ther classified under various orders by different writers. Thus 

 we find that they are given the rank of a family or a sub- family 

 under the Order Perisporiales, Pyrenomycetales, or Sphaeriales. 

 Fortunately plants are not changed by simply changing their 

 name or the name of the group, or by transferring them from 

 one group to another. The Order Sphaeriales is perhaps the 

 best name for the order which includes the plants in question. 



The Ervsiphaceae are characterized by the truly parasitic type 

 of nutrition, the production of large, hyaline, non-septate conidia 



University Stidies, Vol. X. No. 1, January 1910. 



59 



