2 Introduction. 



This succession of spore-forms may be represented graphically by the 

 following diagrams: 



Sporidiolum 



Sporidioluni 



Teleutonport L 4- Aecidlospore 



\^+J 



Uredospore 

 Fio. 1. 



Sporidiolut 



Teleutospore "V 7* Aecidiospore 



^-^T^ 



Teleutospore -*^ f* Uredospore 



Teleutospore 

 Fio. a FIG. 4. 



The first shows the complete cycle of development in which all the 

 spore-forms follow each other in invariable order, and this is the most 

 common form. In the second the uredospore is suppressed, and the 

 number of species undergoing this contracted cycle is much reduced. In 

 the third the aecidiospore is wanting, and the number of forms is still 

 further reduced. And in the fourth the cycle of development is reduced 

 to its lowest limits, a direct succession of teleutospores occurs, and the 

 number of species, instead of reaching a minimum, probably ranks next to 

 those with a complete development. 



The spermatia succeed the sporidiola, and a.re generally present in the 

 life-cycle, but they do not enter into the general development. 



Besides these regular forms, there are others which are generally re- 

 garded as representing either stages in the life-history of imperfectly known 

 species or degraded forms of which only the uredospores or aecidiospores 

 are known. 



The subject, therefore, naturally divides itself into a consideration of 

 the vegetative organs or mycelium and the various reproductive bodies or 

 spores enumerated above, together with the structures accompanying them. 



The life-history of each form, as far as known, will ibe briefly sketched ; 

 but this has still to be investigated in most of the recorded species. 



