408 



BOTANY 



host. Others produce spermogonia and aecidia, and afterwards teleutospores, but 

 no uredospores. In the case of the hetercecious species, it is only possible to 

 demonstrate the connection between the different spore-forms by means of culture 

 experiments. So long as the relation of the different forms was not known, it was 

 customary to designate each by a special generic name ; the Uredo forms as Uredo ; 

 the jEcidia, according to their structure, as Aecidium, Boestelia, Peridermium , 

 etc. The generic name is now determined by the characters of the teleutospores, 

 since theyexhibit the most characteristic distinctions. 



In those Uredineae which no longer possess secidia and spermogonia, the cells of 

 the vegetative mycelium arising from the basidiospore are uninucleate, but subse- 

 quently, before the formation of the teleutospores. binucleate cells are found. 

 Further research is needed to show how the binucleate condition is arrived at ; 

 at all events, these forms exhibit a still further reduction of the sexual process and 

 of the alternation of generations. 



Order 3. Auricularieae 



The basidia, as in the case of the Uredineae, are transversely septate, with four 

 spores. Only a few forms are included in this order. Among the most familiar is 

 Auricularia sambucina (Judas' ear), found on old Elder stems. It lias gelatinous, 

 dark brown fructifications, which are shell-shaped and bear on their inner sides 

 the basidial hymenium. 



Order 4. Tremellineae 



The basidia are longitudinally divided (Fig. 344 JJ). The hymenium is 

 situated on the upper surface of the fructifications, which are generally gelatinous 



and irregularly lobed or folded. 

 The few genera included in 

 this order are saprophytic on 

 decaying wood and tree- 

 trunks, on the surface of 

 which the fructifications are 

 produced. 



Order 5. Hymenomy- 

 cetes ( Kl - 7 '-) 



The basidia are undivided, 

 and bear four spores at the 

 apices of slender sterigmata 

 (Fig. 353 sp). In the simplest 

 forms these basidia spring 

 directly from the mycelium, 

 but in the great majority of 

 cases fructifications are pro- 

 duced, which bear definite 

 hymenial layers, comjiosed, in 

 addition to the basidia, of paraphyses (Fig. 353 p), and also of sterile cystids (c) 

 or club-shaped tubes characterised by their larger diameter and more strongly 

 thickened wall. 



Most of the Hymenomycetes develop their profusely branched, white mycelium 



FIG. 353. Russula rubiii. Portion of the liynifniuin. xh, Sub- 

 hymenial- layer ; ?/. liasidia ; ., sterigmata ; *r. s]mn-s ; /', 

 paraphysps ; c, a cystid. (x 540.) 



