CHAPTER V. COMPARATIVE REVIEW. UREDINEAE. 283 



occurrence of aecidia with fertile spores outside a known typical cycle of development, 

 would in themselves be sufficient ground for supposing that we are here, in the main 

 at least, simply dealing with Uredineae whose course of development is the same as 

 that described above, but is only imperfectly known to us because we have not yet 

 ascertained the conditions for the further development of the particular organs on 

 which the investigation turns. Experience, and especially the discovery of the 

 phenomena of a change of host (section CX), have to a great extent confirmed 

 this supposition ; fresh typical species forming aecidia are being constantly completed 

 out of the separate stages known to us, and we may therefore say with confidence 

 that many of the gaps still existing are only gaps in our knowledge and not in the 

 development of the species. This, it is true, does not exclude the a priori possibility 

 that our scheme does not fit every case. There are perfectly well-known species 

 coming under it, for instance Puccinia Rubigo vera of our corn-fields, which are 

 reproduced year after year in frightful quantities by the uredo only. They produce 

 also millions of teleutospores which germinate but without result, because the 

 sporidia seldom meet with the conditions necessary for developing aecidia. Aecidia 

 certainly are developed if the conditions are favourable ; but the instance shows 

 that the species can multiply abundantly without the interposition of aecidia, and 

 hence there is nothing to prevent the assumption that there may also be species 

 in which the aecidia are not only rare but are altogether wanting ; perhaps they once 

 were there but have been lost, while the other members of the development, 

 uredospores, teleutospores, and sporidia have maintained their existence without 

 changing their former characters. Other species may then have also lost the 

 teleutospores which had become useless to them and become confined to the uredo 

 only. These are at least possibilities which may be cautiously weighed and tested 

 by further investigations. We are led up to them by another path also, which will be 

 discussed in the next paragraph. 



SECTION LXXXII. There are Uredineae of which it may or must be acknow- 

 ledged that the cycle of their development, which is known to us throughout, is 

 different from that of the Uredineae which form aecidia. The species here alluded 

 to are known as the tremelloid Uredineae, to which the Leptopuccinieae and 

 Leptochrysomyxa also belong. 



Organs are known in the tremelloid Uredineae which in structure, development, 

 and germination with formation of sporidia resemble in all essential points the ieleuto- 

 spores of species of Puccinia which form aecidia, and may therefore be called by that 

 name, being distinguished at most from the teleutospores of most of these species by 

 having their spore-membranes as a rule softer and more gelatinous. But this is not 

 always the case ; the aecidia-forming Puccinia Berberidis from Chili, for example, which 

 unfortunately is only known to us from old specimens in collections, agrees in this respect 

 with the Leptopuccinieae which have the softest spores. In this species of Puccinia and 

 in all Leptopuccinieae this character is connected with another peculiarity; the teleuto- 

 spores, or at least the great majority of them, germinate as soon as they mature and 

 while they are still crowded together on the comparatively long stalks by which they 

 are attached to their nutrient substratum. Schroter found that in some species, as 

 Leptopuccinia Circaeae, L. Veronicae, and L. annularis, teleutospores with thicker 

 walls were also formed in addition to the others, and that these cannot germinate 



