CHAPTER V.— COMPARATIVE REVIEW.— UREDINEAE. 285 



of aecidia of their own. But this makes no change in the facts observed in the 

 course of development in the tremelloid Uredineae. 



Schroter distinguishes by the name of Micropuecinia a small group, in which 

 also teleutospores only are known, for instance Puccinia Pruni, P. Aegopodii, and 

 P. Asari. These forms differ from the Leptopuccinieae in the circumstance that the 

 teleutospores drop off" when they are ripe and only germinate after a long rest. 

 We have no complete knowledge of their development. It is possible from these 

 data that it belongs to the tremelloid type, but we must wait for further investigations 

 to decide this point. 



Section LXXXIII. The homologies within the group of the Uredineae are 

 at once apparent from the foregoing account. The organs of the same name are in 

 all of them undoubted homologues in the morphological sense. Starting from Endo- 

 phyllum, the species which are furnished with teleutospores and uredo have a number 

 of members connected by a variety of gradations in the segment between two 

 successive sporidia-generations ; but in the tremelloid forms the homology, as far as we 

 know is interrupted and not restored (see page 125). If, on the contrary, we make the 

 tremelloid forms the starting-point in the comparison, we then have in the case of the 

 species which form aecidia an addition, an acquisition of a new and generally 

 important member of the development, the aecidium with its attendant spermogonia. 



It was pointed out at the beginning of these remarks, that the rhythm of the 

 development in the species which form aecidia is very closely allied to that of the 

 typical Ascomycetes. There is the most complete agreement between the course of 

 development in Polystigma (seepage 2 2 6) and Endophyllum up to the difference between 

 perithecium and aecidium. At present we know of no intermediate forms between 

 these two kinds of sporocarps. But the difference between them is sufficient to make 

 the homology appear questionable. Here is the gap indicated at the outset, for all 

 other peculiarities in the Uredineae which form aecidia are nothing more than special 

 cases of the general course of development in the Ascomycetes. But there are no 

 facts recorded at present which would lead us to infer a nearer connection of the 

 aecidia on any other side than that of the sporocarp of the Ascomycetes, and 

 this circumstance, which is in harmony with the agreement in the general rhythm of 

 the development, to which attention has been repeatedly drawn, turns the scale 

 in favour of assuming that the two are homologous ; anything more than an assump- 

 tion is of course out of the question. But if this assumption is correct, the Uredineae 

 which form aecidia belong to the series of the Ascomycetes, as a special subordinate 

 or collateral group distinguished by special peculiarities of the sporocarp. Further, if 

 the view taken above of the connection of the Ascomycetes with the Peronosporeae 

 and Mucorini, and through them with the general system, is correct, the Uredineae 

 which form sporocarps cannot have been developed from the tremelloid. For 

 the latter therefore there remains only the assumption that they show a retrograde 

 development by the loss of the aecidia, being descendants of aecidia-forming 

 species and apparently homologous with certain segments of their development, 

 sometimes even so like them that they might be mistaken for them. 



Literature. 



Unger, Die Exantheme d. Pflanzen. Wien, 1833. 



The rest of the older writers are noticed in the works enumerated below. 



