VIIl] 



UREDINALES 



205 



produce a second type of uredospore with thick walls which are adapted to 

 survive unfavourable conditions; these are known as amphispores. 



Both aecidio- and uredospores germinate readily and without a rest if 

 fully ripe, but many are shaken off by wind and rain before they reach 

 maturity and remain incapable of germination. Moreover it is stated that 

 spores will not ripen properly on leaves that have been removed from the 

 plant. 



Sooner or later the mycelium of binucleate cells gives rise to teleuto- 

 spores ; these are characteristically grouped together in teleutosori (fig. 1 80), 



Fig. 180. a. PAragmidium Ritbi Vets.; teleutosorus, x 240 ; after Sappin-Trouffy; b. Phragmidium 

 ZJio/aceii//i Wint.; teleutosorus, X240; after Blackman. 



except in the genus Uredinopsis, on ferns, where they are scattered. Like the 

 uredospores the teleutospores are with or without paraphyses and like them 

 arise from rectangular basal cells. They appear as narrow binucleate 

 outgrowths in which one or more divisions take place so that, in the 

 majority of cases, a stalk is formed below and the simple or compound 

 teleutospore is produced above (fig. i8i). The stalk may increase consider- 

 ably in length {Gymnosporangium, Uromyces, Puccinia) or may be very 

 short or absent {Coleosporiitm, Melampsora). 



As already stated the young teleutospore cell is binucleate (fig. 182); 

 when the wall is fully thickened the two nuclei fuse and the spore passes 

 into the resting state. On the renewal of its development two nuclear 

 divisions occur and the gametophytic phase is initiated with the production 

 of the uninucleate basidiospore. 



In the Uredinales the fertilization process thus takes place in two stages, 

 nuclear association being separated by a longer or shorter series of vegetative 

 cells from nuclear fusion. We have here a difference in degree though not 



