822 



INJLTEIOUS INSECTS AND FUNGI. 



[Dec. 1895. 



some seasons are abundant in the fields, and lessen ^the 

 crops in various degrees. This is due to the fungus Ustilago 

 tritici, which is often confounded with the disorder known as 

 " Bunt," Tilletia caries, though essentially distinct. In the 

 latter case the grains alone are affected and spoiled, while sifiut 

 blackens and blasts the whole ear. Oat and barley plants, espe- 

 cially the former, are also liable to smut. The Ustilago affects 

 the organs of reproduction, and it attacks the inflorescence and 

 prevents the formation of grain, turning the whole of the ear 

 into a mass of black powder. It lives upon the parts of the 

 plant designed for fructification and entirely destroys them, so 

 that at harvest time there is no trace of grain or glumes ; only 

 the bare stalk remains blackened somewhat by the spores, most 

 of which have been blown away. Upon examination of an 

 infected ear in the earlier stages of the disorder, it will be seen 

 that the grain at first is much swollen and filled with a thick 

 whitish substance and is permeated throughout by the hyphae 

 or branching filaments of the fungus. After a while the cell 

 walls are broken down and the grain becomes a mass of black 

 spores. The glumes are also disintegrated by the fungus and 

 covered with spores. 



Life History. 



This fungus belongs to the Ustilaginece, or the burning, or 

 charring, fungi, so called because they make plants look as if they 

 were burnt, or charred. It w^as called Ustilago carho by Tulasne. 

 Then it was termed Ustilago segetum by Ballard, and recently 

 it has been described as Ustilago tritici, Persoon, as peculiar to 

 wheat. It was supposed that the same species — Ustilago segetum 

 — attacked wheat, oats, and barley indiscriminately, but the 

 researches of Brefeld, Jensen, and Kostrup have proved that one 

 species of Ustilago is found on oats, another on barley, and 

 a third on wheat. 



The spores of the fungus (as shown at C), are round to ovoid 

 in shape, and rather irregular. They are very small and are 

 produced in enormous quantities. In colour they are black with 

 an olive tinge. They are sown with the seed wheat ; being so 

 minute that they would find an ample resting place in the furrow, 

 or line, on the under part of the wheat grain, as well as in the 

 downy tuft at its extremity. The spores are carried by the 

 wind to the grain while yet in the ears, or during the harvesting, 

 threshing, and winnowing processes. After the grain of wheat 

 has germinated and put forth its plumule from the seed, the spore 

 of the Ustilago sends out a germ tube (D) which makes its vray 

 into the tissues of the young tender shoot. The fungus 

 developes a mycelium, or a series of fine threads, which grows 

 with the wheat stem and finally attacks the grain forming in 

 the ear, which has been the object of its existence in the stems 

 for so many months. The grain is pervaded by the hyphse, or 

 branching arnis of the fungus, and is reduced to a mass of viscid 



