66 FUNGOID DISEASES 



tissue as a result of sexual union ; they are called 

 oospores, and germinate the following spring. 



The above description holds good for P. vicice, 

 except that its oospores have a reticulate thickened 

 outer wall. 



(c) Downy Mildew (^Phytophthora Phaseoli). 

 Class : Phycomycete^ ; Order : Peronosporales. 



Damage to beans and peas may be serious, 

 other plants are also attacked. Greyish-white 

 patches of mycelium appear on the leaves, stems, 

 and pods ; from this mycelium conidiophores arise 

 which bear spores in a similar manner to Phyto- 

 p ht ho 7'a infest mis (see Fig. 21, B, p. 76). The my- 

 celium also penetrates the inner tissue, from which 

 it derives its nourishment. 



Prevention of the dijferent Mildeivs. — 



1. Mow infected clover crops to save what 



remains of them. 



2. Spray with Bordeaux Mixture, repeating 



every fortnight. 



3. Washes of potassium sulphide are very 



effectual, but too expensive. 



4. Burn badly diseased parts. 



5. For attacks of Erysiphe on small areas 



dust with flowers of sulphur. 



6. Drain the land well, for first attacks are 



usually in moist places. 

 II. Rusts. Class: Teliospore^; Order: Ure- 



DINALES. 



