xiv.] SURFACE MILDEW OF TURNIPS. 79 



material streams in threadlike form, and from this thread 

 new clubs immediately arise. Four of these bodies, in 

 different stages of growth, are shown at B, C, D, and E. 

 The surface of one of the organs of transpiration is shown 

 at F, over the opening of which a thread of mycelium has 



This Oidium chiefly injures the turnip by weaving a 

 thick web of mycelium over the organs of transpiration. 

 The spawn effectually stops the passage of watery vapour 

 from the interior of the affected plant, and so puts an 

 end to one of its chief vital functions. The general 

 result is an arrest of growth, and ultimately a poor crop 

 of roots. 



Oidium Balsamii, Mont., is supposed to be an early 

 condition of some more perfect fungus, probably an 

 Erysiphe, such as one sees on the hop, on roses, on mil- 

 dewed grass, and on peas. The two latter species of 

 Erysiphe are referred to in detail farther on in this work. 

 Important as this Oidiuin is to agriculturists, no one at 

 present has worked out its life history or knows whence 

 it comes, where it goes, what other form it takes, or how 

 it hibernates through the winter. The fungus is more 

 prevalent when a humid September follows on a dry 

 August. 



