268 DISEASES OF FIELD & GARDEN CROPS. [CH.XXXIII. 



It unfortunately happens that this parasite is not con- 

 fined to peas ; it sometimes grows on beans and melilot, 

 plants belonging to the same family with the pea. It is, 

 however, able to support itself on plants of St. John's 

 wort, Hypericum; some umbelliferous plants, and the 

 meadow-sweet, Spiraea Ulmaria, L. It is thus capable of 

 growing effectually upon plants belonging to four different 

 natural orders. 



The only known preventive against attacks of this pest 

 is the destruction by fire of all invaded material. The 

 fungus is preserved in decaying refuse ; in this material 

 the little brown conceptacles remain intact during the 

 winter, and in the following summer they burst, and each 

 example discharges about fifty little living transparent 

 spores, as shown in Fig. 124, ready to grow on the leaves 

 of peas, weave a spider-weblike mycelium over the surface, 

 and pierce the epidermis. 



