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A TEXT-BOOK OF BOTANY. 



host results only after the development of resting spores. The 

 mycelia are hyaline, more or less branched, and finally become 

 septate. They send short branches, called haustoria, into the 

 cells of the host, from which they obtain nourishment. Eventu- 

 ally the mycelium becomes much branched, compact and more or 

 less gelatinous through a transformation of the hyphal walls, 

 forming gall-like swellings or blisters on the host. Spores are 

 formed within this gelatinous mass at the ends of the branches 



Fig. 39. 



Corn smut {Ustilago Maydis) showing several gall-like masses of smut full 

 of spores. 



of the mycelium. At a later stage the smut loses its gelatinous 

 character, the mass breaks up, and the spores are freed and dis- 

 tributed as a dry, dusty powder. The spores (primary conidia) 

 are somewhat spherical or ellipsoidal, and are generally separate, 

 but are sometimes united into a mass forming the so-called " spore 

 balls." These are resting spores and upon germination (Fig. 40) 

 produce a promycelium or basidium which becomes septate and 

 from each cell of which conidia called sporidia arise. The sporidia 

 are formed in succession one after another and the process con- 



