198 



PROTOBASIDIOMYCETES 



[CH. 



(sporidium) is formed and receives the nucleus and cytoplasm of the cell 

 from which it arose. 



In Coleosporiuni, Ochropsora, and Chrysospora, nuclear division and 

 septation take place within the teleutospore wall, and the basidiospores are 

 budded out from it, so that the teleutospore cell becomes the basidium 

 directly; in the majority of cases, however, the structure of the teleutospore 

 is not such as readily to allow further growth, and development takes place 

 after the extrusion of the contents as a tubular outgrowth, the so-called 

 promycelium, surrounded only by a delicate membrane (fig. 167). The 

 nucleus migrates into this structure and here nuclear division takes place, 

 transverse septa are formed and the basidiospores are produced. But it 

 must be noted that the nucleus and cytoplasm of the young basidium are 

 those of the teleutospore cell, whether development takes place within the 

 original wall or by means of a promycelium. 



When the basidiospore germinates its germ-tube penetrates through the 

 cuticle of the host and forms a mycelium of uninucleate cells bearing 

 spermogonia and aecidia. 



The spermogonium is usually found on the adaxial side of the leaf; it 

 consists of a group of more or less parallel, unbranched, upwardly directed 

 hyphae, arising from a small-celled tangle below the epidermis or cuticle of 

 the host. 



In the majority of cases the outer hyphae of each group elongate to form 

 paraphyses, so that the spermogonium is restricted in extent, and acquires 

 a flask-shaped or pyriform outline; the paraphyses push up through the 

 ruptured epidermis of the host to project at a narrow ostiole (fig. 168 b). In 



Fig. 167. Gymnosporangium clavariaeforme 

 Rees; germinating teleutospores; x 666. 



Fig. 168. a. Phragmidiuin violacaiiii 

 Wint., X330; b. Gyninosporangitim 

 c/aiariae/or>ne Rees, X'26o; sper- 

 mogonia; after Blackman. 



