CHAPTEE XIV. 



SURFACE MILDEW OF TURNIPS. 



Oidium Balsamii, Mont. 



THE mildew of turnips, named Oidium Balsamii, Mont., 

 is often confounded with the true putrefactive mildew of 

 the cabbage tribe, named Peronospora parasitica, Pers. 

 The two are indeed so much alike to the unaided eye 

 that it is often impossible for even an experienced ob- 

 server, without a lens, to distinguish one from the other. 

 As if to make the subject still more involved, it fre- 

 quently happens that the two fungi grow in company on 

 the same host plant. They are, however, wholly dis- 

 tinct from each other, both in habit and structure. 



The name Oidium is derived from the Greek oon, an 

 egg, and eidos, resemblance, and refers to the usual egg- 

 shaped form of the spores or conidia. In the present 

 instance the generic name is not very appropriate, for the 

 conidia are somewhat barrel-shaped. The specific name 

 Balsamii was given in honour of Balsamo, a Milanese 

 gentleman, who first noticed the species. When first 

 detected the fungus was growing on a Continental species 

 of Mullein, named Verbascum montanum, Schrad. We 

 have this plant in our gardens, but the fungus is more 

 common here on the Black Mullein, Verbascum nig- 

 rum, L. ; it also grows on cultivated strawberries. In 

 the latter case the fungus makes its first attack on the 

 leaves, and then speedily invades with increased vigour 

 the flowers and footstalks, ultimately inducing the 

 wretched appearance so well known in connection with 

 grape vines when attacked by the allied fungus named 



