18G Gku-fiths: Common TaRasite of Powdery Mildews 



place to include the following description based on specimens from 



both Europe and America. 



Mycelium variable, hyaline to fuscous, within the mycelium of 

 species of Erysiphaccae and occasionally in the tissues of the host 

 plant (Fig. 1 6), 4 to 8 (usually 4 to 5) // in diameter; pycnidia 

 very variable in size and form, membranous, oval, pyriforna to 

 globular, fuscous to brown, produced in horizontal mycelium 

 (Fig. 8)' conidophore (Fig. i-;), or perithecium (Fig. 10-12); 

 spores hyaline, oblong, often slightly inequilateral, biguttulatc when 



y2-ioy, X 3>^-6// (Fig. 15). 



There occurs in the various descriptions of this species, under 

 different names, a wide variation in characteristics which in many 

 groups would establish good species, and indeed might here were 

 it not for the extreme variability of single specimens. In some 

 cases the pycnidia have been described oval to pyriform and 

 stipitate, and in other cases globular. The accompanying figures 

 will clear away all doubt regarding the possibility of such a varia- 

 tion and explain how it occurs. In my specimens on Grindclia a 

 variation of fifty l>- in size of the perithecla may often be found in 

 the same microscopic field. A great discrepancy also occurs 

 in the measurement of spores by various observers ; when, how- 

 ever, the specimens from which these measurements were made 

 are compared with one micrometer scale they are reduced to the 

 limits easily attained in any species. Descriptions vary also in 

 the matter of guttulation of the spores, some being described as 

 guttulatc and others as continuous. My specimens on Grindclia 

 and Lygodcsmia show both of these conditions in different stages 

 of development. When mature the spores always show the char- 

 acteristic guttulae. One may, by squeezing young pycnidia under 

 the cover slip, see small, oval, globular or Irregular continuous 

 cells. A study of De Bary's figures of the spore' development 

 will easily show that these are nothing more than the young 

 spores imperfectly formed, or In some cases simply cells of the 

 pycnidia. In examining some of the herbarium material at hand, 

 especially European cxsiccati, this phenomenon was often met with. 

 Careful examination of my own material collected early in the 

 season showed the same peculiarity ; and In some exsiccati, notably 

 Cicinobobis cotoncns Pass., both mature and immature pycnidia 

 were common. 



