CH. XXXIII.] 



PEA MILDEW. 



267 



FIG. 124. 

 PEA MILDEW. 



siphe Martii, Lk. 

 Enlarged 500 dia- 

 meters. 



numerous stomata as at A A A. The conceptacle or peri- 

 thecium is distinctly smaller in size than in E. graminis. 

 D.C., as illustrated in Fig. 57, and the cells forming the 

 bark of the conceptacle are larger. Each 

 conceptacle contains four or eight spor- 

 angia or spore cases, and each sporangium 

 carries four to eight sporidia, as shown 

 at Tig. 124, enlarged 500 diameters ; 

 this illustration may be compared with 

 Fig. 60. The conceptacles arise from a 

 dense woven mass of very fine white 

 mycelium, omitted in Fig. 123 in 

 favour of the epidermis of the leaf with 

 its stomata. This mycelium is woven 

 all over the stomata, and so one of the Sporangium or ascus, 

 chief vital functions of the leaf, the with spores, of .Ery- 

 transpiration of vapour, is arrested. 

 The fungus grows on both sides of the 

 leaves. 



This destructive blight of peas invariably invades the 

 late varieties, and is especially virulent in dry seasons. 

 In small gardens the attack of the fungus may be pre- 

 vented by keeping the peas well supplied with water. 

 This treatment, however, cannot be adopted in the fields, 

 and watering favours the growth of the Peronospora last 

 described. Sometimes late peas are so badly attacked by 

 this fungus that they appear as if thickly dusted with 

 powdered chalk, and on the white surface thus formed 

 the innumerable black conceptacles of the Erysiplie may 

 be readily seen with the unaided eye. An attack of this 

 fungus generally stops the growth of the invaded plants, 

 and makes the production of pods impossible. The 

 mycelium is provided with the minute suckers termed 

 haustoria, and these haustoria pierce the epidermis of the 

 attacked plant and cause decay. We have seen this 

 fungus growing with its conceptacles inside the pods of 

 peas. 



