32 Origin of Spore-forms. 



SPORIDIOLUM. 



The sporidiolum was probably the earliest form of rust spore, and 

 represents the transition from the saprophytic to the parasitic mode of life. 

 If we start from undoubted saprophytes, the passage from the one to the 

 other will be made clear. It was not only necessary for the spread of these 

 fungi that the spores should germinate rapidly, but that they should be 

 produced in sufficient numbers, and so the basidium, or parent cell, had 

 either to produce more than one spore or divide up into several cells. In 

 accordance with this, in one type, the one-celled basidium produces mostly 

 four spores (Fig. 9) ; in another type the basidium divides usually finto 



FIG. !). 



four cells, each cell producing a spore. The latter type is well seen in 

 the Auriculariaceae where in such a genus as Saccoblastia the basidia are 

 transversely septate, and each cell bears a sterigma with its spore (Fig. 10). 



FIG. 10. 



Turning now to a parasitic genus such as Coleosporium, there is a close 

 resemblance in the mode of formation of spores. The body called the 

 teleutospore is found to consist of four cells 1 placed one above the other, 

 and each cell gives rise to a sterigma, with a sporidiolum at the end of it 

 (Fig. n). This is something very different from the typical teleutospore, 



FIG. 11. 



in which each cell produces, not an ordinary undivided germ-tube but a 

 promyceltum divided into four cells, each of which bears a sterigma with 

 a sporidiolum. The so-called teleutospore of Coleosforium is evidently 

 the representative of the septate basidium in the Auriculadaceae, although it 

 s generally considered to be an exceptional form of teleutospore, which 

 occurs in other genera of Rusts as well, such as Ockrojtsora, Trichofsora, 

 and Chrysopsora. If the basidia in one of the saprophytic Auriculariaceae, 

 s Saccoblastia ovtspora Moell., are compared 'with those of the 

 parasitic Coltosponum senecionis, there is seen to be complete agreement in 

 the structure. 



