19 



formed in the autumn from a homogeneous mass (Fig. 5A), In spring 

 this mass differentiates and produces in its interior G to 8 elliptical asco- 

 spores which under favorable conditions germinate like condidia and begin 

 again the cycle of vegetation of the Erysiphe (Fig. 5B). A good section 

 of a perithecium in our laboratory showed three asci, only, the others being 

 concealed in the cavity of the perithecium left intact by the razor. 



Injuries caused by Erysiphe graminis, 



m our selection plots wheat, rye and barley have suffered the greatest 

 injury by this disease. Alone or sometimes with other fungi, such as 

 Helminthosporium, Puccinia, etc., it takes possession of a part of the sur- 

 face of the epidermis, and thrives at the expense of the food materiaia 

 of the host plant, besides probably preventing the proper functioning oi 

 chlorophyll in the parts of the leaf occupied by the spots. 



Curative and Preventive Remedies. 



l^'rom 1885 to 1889 the disease appeared in the neighbourhood ot 

 tstockholm with such intensity that the cultivation of cereals was seriously 

 threatened. Prillieux cities the applications of flowers of sulphur as a 

 curative remedy that the farmers of Stockholm employed to save their 

 irops. In France the application of flowers of sulphur against the grape 

 disease (Uncinula spiralis or Oidium Tuckeri), caused by a fungus analo- 

 gous to the Erysiphe, has given very good results. 



In particular instances like that of our selection plots it is possible to 

 scatter flowers of sulphur on the leaves of affected plants, nevertheless, 

 sulphur application to a large crop, although possible, meets with practical 

 difficulties. For this reason it is scarcely recommended. 



The most effective means of controlling the disease seems to be rather 

 one of prevention. It consists in the creation of resistant varieties. This 

 can be attained by the choice of stalks that have not been attacked by the 

 fungus. In making the selection it is therefore of importance to avoid 

 selecting the heads borne by plants occupying the borders of the plots, 

 inasmuch as they are more exposed to the disease. 



In late summer or at the beginning of autumn the spontaneous vegeta- 

 tion of weeds and of seed shelled from the cereal occupying the ground is 

 covered by a white down which appears like a coating of milk of lime 

 sprinkled on the leaves. The humidity produced by dew of the cool nights 

 favors the development of Erysyphe. 



Moreover, the destruction of these weeds makes necessary the tillage 

 of the land before the work of autumn. It may be well to add that the 

 growing of the same cereal on the same land for two or more consecutive 

 years tends to increase the grievous consequences of this disease. 



