UREDINEAE AND HYMENOMYCETES 527 



Hymenomycetes are mostly saprophytes and also with the fact that, 

 every autumn, dead leaves, stems, and other structures which are 

 discarded or broken away from Phanerogams form a new and rich 

 substratum for saprophytic mycelia. Moreover, the damp autumn 

 months constitute an admirable time for the infection of new sub- 

 strata of this kind by the liberated spores. 



We now come to the discussion of the form of the basidium in 

 the Hymenomycetes and in the Uredineae ; but, for the present, we 

 shall exclude from the former the Auricularieae and from the latter 

 the Coleosporieae, for the Auricularieae and the Coleosporieae are 

 exceptional in the nature of their basidia and will be treated of later. 

 Let us compare the basidium which is typical for the Agaricineae, 

 Polyporeae, etc., with that which is typical for Puccinia, etc. In the 

 Hymenomycetes, the basidium is typically club-shaped : its central 

 axis is straight ; and it bears terminally four sterigmata and four 

 spores. In the Uredineae, the basidium is less compact ; it is usually 

 somewhat elongated and bent at the end so that its whole form is 

 sickle-shaped, its axis being curved ; and it bears four sterigmata and 

 four spores laterally ; the position of the sterigmata is always on the 

 convex side of the sickle. If we regard the interior of the mature 

 basidia, we observe that, in the Hymenomycetes, the basidium 

 is usually non-septate ; whilst, in the Uredineae, septa divide the 

 basidium into four cells which lie in a hnear series. The septate 

 condition of the basidium and the lateral position of the spores in the 

 basidium of the Uredineae has often been commented upon and con- 

 trasted with the non-septate condition of the basidium and the 

 terminal position of the spores in the Hymenomycetes ; but, so far 

 as I am aware, no one has remarked upon the fact that in the Ure- 

 dineae the basidium is typically curved whilst in the Hymenomycetes 

 the basidium is typically straight. The fact that the Uredineae have 

 curved basidia has been frequently noticed, and various observers, 

 from Tulasne and de Bary onwards, have published drawings 

 showing incidentally that the basidia of numerous species of Ure- 

 dineae are curved at their ends more or less semi-circularly ; but no 

 one seems to have asked the question : what is the physiological 

 meaning of the curvature ? 



The question that we shall now attempt to answer is therefore : 



