Systematic Arraiigojwiit. 145 



outside the host-plant, and, as a rule, produces a germinal tube only once, 

 but the conidia formed multiply indefinitely by direct sprouting or budding. 

 This sprouting of the conidia in a yeast-like manner goes on until the nutri- 

 ment is exhausted, and then they develop slender filaments, which, if tliev 

 reach the host-plant at the proper stage, enter in and form the large septate 

 spore-producing mycelia. 



We have here the formation of different reproductive bodies inside and 

 outside the host-plant. Inside a mycelium is produced, which finally gives rise 

 to spores, and outside, the conidia, formed from the germination of the spore, 

 sprout and multiply indefinitely. This continuous sprouting in a nutritive 

 solution is the counterpart of the mycelium-forming spores confined to the 

 host, and the germination of the conidia to form slender filaments in the 

 exhausted solution is the connecting bridge between the outside and inside 

 development. It may be represented graphically thus : — 



'Sprouting Conidia 



Outside Host-plant 

 (Saprophyte) 



Inside Host-plant 

 (Parasite) 



While this is the general course of development, there may be slight 

 deviations from it. In the American corn smut [Usiikup zeae) the 

 sprouting conidia may not only occur in the fluid, but in the air, as aerial 

 conidia. In Tilletia and other genera, not only is a whorl of conidia produced 

 at the apex of the germinal tube, but the conidia may form in the air a 

 mycelium like a tuft of mould, from which sickle-shaped aerial conidia again 

 arise, singly and irregularly (Fig. 5). In Entyloma there is the further 

 peculiarity that, in addition to the ordinary promycelial conidia, there are 

 tufts of conidia produced on hyphae projecting from the host-plant itself. 



It may finally be noted that infection through the flower, which is the 

 only mode known in the loose smut of wheat and the naked smut of barlev, 

 is probably the most advanced form in which it occurs. The young ovary 

 is not only attacked in its earliest stages, but the embryo itself is permeated 

 by the fungus filaments, which are secure within the seed, and only await 

 the germination of the seed to develop within the host-plant and produce 

 its spores. The climax is reached in the Anther smut of the Carnation 

 family, where the uncertain and wasteful dispersion of the spores by the 

 wind is no longer relied on, but insects carry thein from flower to flower as 

 in the process of pollination. 



The order may be grouped in two I'amilies. both of which are represented 

 in Australia, and are distinguished by the mode of germination of tlie spores 

 and the production of conidia. 



FaM. 1. ITSTILAUIN-ACE^ Tul. 



This family is characterized by the spores germinating by means of a 

 septate promycelium, which produces lateral and terminal conidia. The 

 genus Ustilago, from which the family is named, is the richest in Australian 

 species, and of the ten recognised genera, six of them have been found here, 

 viz. : — Ustilago, Melanopsichium, Cintractia, Sorosporium, Thccaphora, and 

 Tolyposporium. 



