CRYPTOGAMS 



403 



of the germ- tubes (Fig. 347 C). When abundantly supplied with food material, the 

 germ-tubes grow into large mycelia, from which such sickle-shaped conidia are so 

 abundantly abstricted that they have the appearance of a growth of mould (Z>). 



FIG. 347. Tilletia Tritici. A, the basidium developed from the brand-spore bearing at the end 

 four pairs of spores A: (x 300) ; B, the dispersion of the spores which have fused in pairs ( x 

 250) ; C, one of the paired spores germinating and bearing a sickle-shaped conidium sk (x 400). 

 D, Mycelium with sickle-shaped conidia (x 350). (After BREFELD.) 



Thus Tilletiii, unlike Ustilago, produces conidia of two forms ; but in other 

 particulars the development of both groups is the same. 



The young resting-spores, and the cells of the mycelium from which they are 

 produced contain each two nuclei which fuse with one another as the spore becomes 

 mature. The cells of the basidia, and the basidiospores are all uuinucleate, only 

 the secondary conidia of Tilletia being again binucleate. 



Order 2. Uredineae (Rust Fungi) p-? 8 ) 



. The mycelium of the Uredineae lives parasitically in the intercellular spaces of 

 the tissues of the higher plants, especially in the leaves, and gives rise to the 

 widely spread diseases known as Rusts. Their more varied spore- formation is a 

 distinguishing feature as contrasted with the Ustilagineae. 



As in the latter order, the basidia are not produced directly on the mycelium 

 but on the germination of a special type of spore, teleutospores or winter spores, 

 which are characteristic of all Uredineae. The teleutospores arise in small clusters 

 beneath the epidermis of the diseased leaf from the ends of hyphse ; frequently 

 two or more form a short chain. They are thick- walled resting-spores and persist 

 through the winter (Fig. 348, 1, ot). The group of spores usually bursts through 

 the epidermis. At first the spores, like the cells of the mycelium which bears 

 them, have two nuclei, but the nuclei fuse before the spore is ripe. 



In the germination of the teleutospore a basidium (promycelium) grows from 

 each cell (Fig. 348, 2) ; it becomes divided by transverse septa into a row of four 

 cells from each of which a sterigma bearing a single uninucleated basidiosjwre 

 (sporidium) is produced. The sporidia are dispersed by the wind and germinate 

 in the spring on the leaves of host plants (which may be of the same or different 

 species from the one on which the teleutospores were produced), giving rise to an 

 intercellular mycelium, all the cells of which are uninucleate. From this 

 mycelium organs of two kinds arise, spermogonia on the upper surface of tin- leaf 

 and secidia on the lower surface. 



2 D 1 



