DISEASES OF THE SKIN. 265 



plant that bears them, and also greatly inclined to turn 

 red. The acid they contain is partly acetous, but more 



of the astringent kind. 



The diseases of the skin, to which many vegetables 

 are subject, are less easily understood than the forego- 

 ing. Besides one kind of Honey-dew, already men- 

 tioned, p. 144, something like leprosy may be ob- 

 served in Tragopogon major, Jacq* Austr. t. 29, 

 which, as I have been informed by an accurate ob- 

 server, does not injure the seed, nor infect the progeny. 

 The stem of Shepherd's Purse, Engl. Bot. t. 1485, is 

 occasionally swelled, and a white cream-like crust, 

 afterwards powdery, ensues. The White Garden 

 Rose, Rosa alba, produces, in like manner, an orange- 

 coloured powder. It proves very difficult, in many 

 cases, to judge whether such appearances proceed from 

 a primary disease in the plant, arising from unseason- 

 able cold or wet, or are owing to the baneful stimulus 

 of parasitical fungi irritating the vital principle, like 

 the young progeny of insects as above related. Sir 

 Joseph Banks has, with great care and sagacity, traced 

 the progress of the Blight in Corn, Uredo frumcnti, 

 Sowerb. Fung. t. 140, and given a complete history 

 of the minute fungus which causes that appearance. 

 See Annals of Botany, v. 2. 51, t. 3, 4. Under the 

 inspection of this eminent promoter of science, Mr. 

 Francis Bauer has made microscopical drawings of 

 many similar /w??7 infecting the herbage and seeds of 

 several plants, but has decided that the black swelling 



