132 DISEASES OF FIELD & GARDEN CROPS. [CH. 



1000 diameters, in the act of germination at C. The 

 asci and sporidia of Peziza postuma (B. and Wils.), illus- 

 trated to the same scale in Fig. 9, may be referred to for 

 comparison of size and form. 



The autumn-borne perithecia do not burst and set free 

 their contained sporidia during the autumn in which they 

 have been formed, but they fall to the ground with the 

 decaying grasses on which they have lived during the 

 summer. They rest on the ground during the winter, 



x 



FIG. 60. 



Asci and Sporidia of Erysiphe graminis, B.C., enlarged 500 diameters. 

 Germinating Sporidium, enlarged 1000 diameters. 



and the hard wall of the perithecium effectively protects 

 the contained asci, and the asci in turn protect the 

 tender sporidia against all ordinary frost, dryness, or damp. 

 No sign of life can be detected in the fallen perithecia till 

 the following spring or early summer, and then, if old 

 decaying grass or straw is searched over, the perfectly un- 

 injured perithecia may be found. In the early summer 

 these bodies burst on the ground, as illustrated at Fig. 61, 



