DISEASES OF PLANTS. 143 



leaves and chaff, and when the spores have burst through the 

 outer covering they are readily dispersed. A fungus closely 

 resembling this is called by botanists, Puccinia graminis, or mildew, 

 and its resemblance is so great to some forms, or stages of Rust, 

 that they have been frequently taken for each other. The latter 

 parasitic fungus has little dark brown, club-shaped spores, having 

 tlie thicker end divided into two chambers, each filled with 

 sporules. They taper gradually into a fine stalk at the base. Both 

 these fungi make their appearance in little cavities, seated 

 immediately beneath the pores of the leaves, which certainly looks 

 very much as if the sporules entered there. The pores, or 

 stomata, of the loaf, are naturally exhaling organs, continually 

 discharging under the influence of light, a large proportion of 

 the water imbibed by the root. But in moist weather this function 

 is impeded, if in some cases it be not actually reversed ; when it 

 would be easy for the almost invisible sporules to enter these 

 invisible stomata with the moisture imbibed by them. A generally 

 healthy state of the plant, without any over-luxuriance of vege- 

 tation, which we saw early in this hour, was a diseased state of 

 the plant, is most likely to secure a crop against the attacks of the 

 rust and mildew fungi. 



A notion has long prevailed in England, but not on the Continent, 

 that the barberry bush (Berboris vulgaris) is in some way or 

 other frequently connected with the production of mildew in 

 wheat. Now whenever you find a general belief in an assorted 

 phenomenon, you may be pretty sure that it has a basis of truth, 

 and that the apparent phenomenon is a reality. In the present 

 case practical men are by no means woll agreed as to this 

 statement, and they are not unanimous in denouncing the barberry. 

 Some experiments by Staudinger at Flotbock, seem to contradict 

 the opinion so generally received. Staudinger and Horneman 

 planted wheat and surrounded it with barberry bushes, and 

 repeated the experiment several times without obtaining any 

 mildew. Mr. Knight, an English botanist, obtained negative 

 results in experiments of the same kind. Professor Henslow says 

 that in the only case of barbeny growing near wheat, ho found 

 the wheat more mildewed than at any other point. Now the best 

 way to reconcile these different opinions is to experiment with 

 wheat and mildewed barberry. It will then satisfy the experi- 

 menter that the fungus of an infected barberry will produce by 

 migration a disease in the wheat near it, and that a sound barberry 



