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 @ przor? 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 
Leptochrysomy<xa 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 zelewto- 
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. Schröter 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 
