Origin of Spore-forms. 31 



CHAPTER XI. 



ORIGIN OF THE PRINCIPAL SPORE-FORMS. 



The most characteristic feature of the Uredineae and that which renders 

 them specially interesting is the variety of spore-forms which they pro- 

 duce. But while on the one hand there is a regular succession of spore- 

 forms, on the other the number may be reduced even to a single kind, and 

 the question arises in such cases whether the missing spore-forms have 

 dropped out of the course of development, or whether they have never been 

 iormed. Since, as we shall see, there is every reason to believe that the 

 various spores originated from a primitive form, the natural conclusion 

 would be that where they do not occur they have not yet been developed, 

 yet there are cases where intermediate forms may have been suppressed, 

 judging by what obtains in closely allied species. 



In all rusts whose complete development is known there is one kind of 

 spore which is invariably present, and which serves to distinguish the 

 various genera, and that is the teleutospore. But the teleutospore on 

 germination gives rise to another kind of spore, the sporidiolum, which 

 may be regarded as the starting-point of the life-cycle, just as the teleuto-. 

 spore is the last-formed or finishing spore. 



The simplest form of spore, using this term in its widest sense, was at 

 first developed from any joint of the exposed hyphal filament, but ulti- 

 mately as the differentiation between the vegetative and reproductive por- 

 tions of the fungus became more marked, the point of origin was restricted 

 to a definite spot of an upright hypha towards the apex. By a process 

 of abstriction, the end of the hypha was rounded off and detached by simple 

 contraction without the formation of any septum. These might either be 

 produced solitary or several formed in succession, constituting a chain. 

 (Fig. 7 a, b.) 



b. 

 FIG. 7. 



The spore might also originate by budding, as in the case of the 

 Yeasts, where a small protuberance quickly grows to its full size, becomes 

 rounded off, and detaches itself. In this process of budding the pro- 

 tuberance often narrows 1 itself at the point of attachment into a slender 

 stalk, whereby the connexion with the parent cell is maintained until the 

 spore is fully formed. (Fig. 8.) 



FIG. 8. 



This short delicate stalk proceeding from the parent cell is known as a 

 sterigma, and either by abstriction or budding the origin of the various 

 spore-forms may be explained. 



