THALLOPHYTA. 675 



chlamydospores only germinate after they have been distributed, and in a very 

 characteristic manner. A short tube is formed, and from this (the promycelium or 

 basidium, of. p. 674) conidia ( = sporidia) are abstricted. In the Ustilaginaceae this 

 basidium is septate and the conidia are abstricted laterally ; in the Tilletiacese the 

 basidium is non-septate, and the conidia are abstricted as a crown at the apex. This 

 is the main difference between the two families. The conidia, which are budded 

 off from the promycelium, have the power of budding in a suitable soil with enor- 

 mous facility, forming new conidia, and this may be continued for a considerable 

 time. In this way the soil becomes thoroughly infected, and should a young seed- 

 ling host-plant arise, it is almost certain to be penetrated and invaded by one of 

 these germ-like conidia. 



Ustilaginaceae. — These are the Smut-fungi properly speaking. Ustilago segetvmi 

 ( = Ustilago carho), the common Smut of Wheat, Barley, Oats, &c., has been very 

 fully investigated. The cereals in question become infected when quite young by 

 the tiny conidia, which put out delicate germinal tubes and penetrate the young 

 growing tissues. Should the young plants escape infection at this stage, they are 

 safe against the parasite, which cannot penetrate the hard, adult tissues. The tubules 

 of the Ustilago penetrate from cell to cell, and take up their position at the growing 

 point. Here they keep pace with the growth of the host, but the presence of the 

 parasite is not manifest externally until the grain begins to ripen. As the grains 

 begin to swell, the fungus increases rapidly, and occupies the greater portion of their 

 substance with its mycelium. It thrives, of course, at the expense of the food which 

 would otherwise have served in forming the embryo and reserve of food-material in 

 the seed. Finally, the Fungus resolves itself into masses of black chlamydospores — 

 the " smut " — which appear between the glumes of the ear. These chlamydospores, 

 as already stated, after a period of rest, produce their promycelia and bud off 

 conidia, which in turn bud off other conidia, and so the ground is kept infected. It 

 was formerly a matter of mystery how the Fungus got into the host-plant, as traces 

 of it were not recognized till it burst out in the ripening ear in the " smut " stage. 

 It is only comparatively recently that the period of infection has been recognized, 

 and the fact that the mycelium grew up, so to speak, with the host-plants was fuUy 

 realized. Ustilago Maydis produces hypertrophied growths on the Maize, and has 

 been alluded to in a former chapter (cf. p. 624). Ustilago violacea attacks the 

 stamens of many Caryophyllacese, developing its chlamydospores in place of pollen 

 in the anthers. Ustilago longissima is very common in the leaves of the aquatic 

 Grasses Olyceria aquatica and G. fiuitans; it produces its chlamydospores as long, 

 parallel, black lines. 



More than 60 Ustilagos have been distinguished ; a large number of them attack 

 cereals and other grasses. 



Tilletiacece. — Have on the whole a life-history resembling the TJstilaginese ; their 

 main point of difference residing in the fact that the promycelium is unsegmented, 

 and produces its conidia in a crown at the apex. Tilletia Tritici attacks wheat. In 

 Urocystis the spores are clustered into little balls, the accessory spores forming a 



