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BOTANY 



PART II 



origin. The mycelium continues its development in the inflorescence, and 

 ultimately terminates its existence by the production of brand-spores. 



In addition to the infection of young plants, either resting-spores or the conidia 

 resulting from their germination may be carried to the stigmas of the grass-flowers 

 and germinating there produce a mycelium which penetrates to the young seeds 

 and passes the winter in the embryo-plants. Such infection of the flowers may 

 alone take place as in Ustilago Tritici, U. Hordei, and U. antherarum, or the seed- 

 ling may more often be infected as in U. Avenae, U. Sorghi, U. Panici miliacei, 

 U. Orameri. The Smut of Maize can infect all parts of the plant while in a young 

 state and the disease is limited to the infected spots. 



The life-history of the Tilletiaceae is similar to that of the Ustilaginaceae. The 

 best-known species are Tilletia Tritici ( = T. Caries) and Tilletia laevis, the fungi 

 of the stink-brand of wheat. The resting-spores fill the apparently healthy grains 

 and smell like decayed fish. In the first-named species the resting-spores are 

 reticulately thickened ; those of T. laevis, on the other hand, are smooth-walled. 



FIG. 401. Tilletia Tritici. A, The basidium developed from the brand-spore bearing at the end 

 four pairs of spores k (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.) 



Unlike the Ustilaginaceae, the germ -tube gives rise only at its apex to filiform 

 basidiospores, which are disposed in a whorl, and consist of four to twelve spores 

 (Fig. 401 A). The basidiospores also exhibit the peculiarity that they coalesce with 

 one another in pairs in an H-form. The filiform spores germinate readily, and 

 produce sickle-shaped couidia at the apex of the germ-tubes (Fig. 401 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 (D). Thus Tilletia, unlike Ustilago, 

 produces conidia of two forms ; but in other particulars the development of 

 both groups is the same. 



As regards the behaviour of the nuclei, in the Ustilagineae the young spore 

 as a rule has two nuclei which then fuse. In the germination of the spore a 

 reduction division may therefore be anticipated. The cells of the promycelium 

 and the sporidia are uninucleate and mark the commencement of the haploid 

 phase. The binucleate condition is again attained in various ways. In U. Maydis 

 the parasitic mycelium consists of uninucleate cells until, shortly before the 

 formation of spores, neighbouring cells of the hypha fuse and thus the binucleate 



