The Scottish Naturalist. S3 



seedlings of the common oat infected with ALcidium spores from 

 Rhamnus producing the Uredo of Puccinia coronata. 



That these experiments are very remarkable in the uniformity 

 of their results, and that they afford, in the hands of so careful an 

 observer as Mr. Plowright, a very strong support to the theory of 

 Hetercecism, cannot be disputed ; and yet they raise other diffi- 

 culties by their very success. It is very hard to see why, for ex- 

 ample, ALcidium Tussildginis should be so common, while its 

 alternate form, Puccinia Poarum on this theory, had not previously 

 been recorded from Britain, though both host-plants are extremely 

 •common ; and this is but one case out of many in our present 

 knowledge, or rather ignorance, of the life-history of the Uredines. 

 Again, Puccinia graminis is known to be exceedingly injurious to 

 "wheat in places where Barberries are few and widely scattered, or 

 even where they do not occur. From the analogy of the E?itozoa 

 among animals, it would naturally be expected that for the welfare 

 of hetercecious fungi both host-plants ought to be within reach of 

 the spores ; and that the fungus would soon disappear from any 

 locality unfavourable in this respect. It would also be only 

 natural to suppose that it should occur, of course in its corres- 

 ponding generation, in proportionate frequency on both host- 

 plants, yet we see that such is not the actual state of matters. It 

 is evident that our information as yet is very fragmentary, and that 

 there is great need of further observations to throw light on the 

 darkness that still surrounds these fungi. 



Throughout the vegetable kingdom, as all botanists are aware, 

 the most useful and reliable characters on which to found the 

 classification of any group are those obtained from the modes of 

 development and reproduction. Hence it is only what may be 

 looked for that the relations claimed to exist between the various 

 forms of spores in the Uredines, and the cycle of development 

 indicated in such experiments as Mr. Plowright's, should be made 

 the basis of a classification to supersede the very unsatisfactory 

 one that has gradually grown up in that group, and that an attempt 

 should be made to establish somewhat more natural genera than 

 has been possible hitherto. Accordingly, we find that in the 

 latest work treating of the Uredines of Central Europe (Winter's 

 " Pilze " in Rabenhorst's " Kryptogamen-flora von Deutschland, 

 'CEsterreich und der Schweiz "), they are broken up into genera on 

 this basis, and that the number of genera is considerably reduced, 

 while at the same time they are better characterised and more 

 readily recognised than in earlier works. Necessarily there are 

 many points that must yet be worked out before we may hope for 

 ;a perfectly satisfactory system of grouping these plants, and a good 

 deal may be said still on both sides of the vexed question of Heter- 

 cecism ; but enough is known, and admitted by all, to prove that 

 many of the fungi that have been described, and that are still 

 retained in systematic works on these plants, as distinct species 



