On the Fiunji prodiici7icj Rust and Mildew. 



221 



remarks tends to show that each form of spore (I mean the spo - 

 ridia of Uredo rubigo and Puccinia cjramims) had been traced by 

 himself from its earliest stage to a complete state of development;, 

 without his observing any transformation of one form into the 

 other. He admits^ however, that the two forms do occur toge- 

 ther, and that those of the Puccinia are frequently found in the 

 very spots previously occupied by those of the Uredo. I do not 

 entertain the least doubt of the accuracy of M. Vilmorin's observ- 

 ations; but I do not consider them conclusive e\-idence against 

 my own opinions, which are founded on observations of anothei 

 class. If it be true that both forms of spore may be developed 

 from the same spawn (mycelium), then we may suppose that the 

 precise circumstances which induce the development of one form, 

 must vary in some respects from those upon which the production 

 of the other form depends. The two forms, then, may not 

 alwa3'S appear simultaneously, or even exactly in the same places, 

 on a plant infected by the fungus. If, however, there should 

 chance to be such a combination of circumstances as is more or 

 less favourable to the development of both forms, then we might 

 not only expect to find them intermixed, but might even hope to 

 meet with certain intermediate forms which would establish their 

 connexion and prove the identity of their origin. Now this, as I 

 conceive, is precisely what I have had an opportunity of witness- 

 ing. I propose, therefore, with as little technicality as possible, 

 to lay the result of these observations before the Society ; but I 

 must still recommend botanists to re-examine the subject. All 

 microscopic observations should be repeated by more than one 

 pair of eyes, so liable is every one to misapprehension and decep- 

 tion when using lenses of high powers. I would also suggest 

 our making diligent search for analogous cases, in order to see 

 whether there may not be other Uredines which are reducible to 

 imperfect states of Puccinicu or to species of other allied genera. 

 I have already stated my own convictions with respect to the iden- 

 tity of Uredo Roses and Aregma mucronata. 



All the little patches or masses of spores (i. e., the sori com- 

 posed of sporidia) in the specimens to which I am referring, were 

 developed on the inner surface of the chaff-scales (glumce and 

 pale(B). In plate V. I have given an enlarged representation of 

 an outer scale (pcdea inferior) of a flower of wheat. The sori 

 scattered over it have raised the skin (epidermis) into blisters, 

 which are most frequently of an oval form. 



In an early stage of the disease these were all of a pale yellow, 

 varying to an orange tint : later in the season blisters were raised, 

 varying from brownish-yellow to a dark-brown ; many had a 

 peculiar waxy appearance ; some of the blisters were pardy yellow 

 and partly brown ; most of the early formed yellow blisters burst. 



