FUNGI. USTILAGINEAE. 87 



in T. laevis. Urocystis is distinguished by the peculiar behaviour of its spores. These 

 appear as enlargements of certain branches of the threads of the mycelium, and occur 

 singly or in groups ; then special branches of the mycelium grow at an early period 

 round the group of spores, or the single spore, and form an investment for it ; the 

 cell-wall of the spores is thick and of a brown colour. Urocystis occulta is a parasite on 

 the leaves and stems of rye. The mycelium vegetates at first in the intercellular spaces 

 of the plant, but afterwards pierces the cell- walls. Germination is similar to that in the 

 two species above described, only the H-shaped union of the sporidia occurs but 

 seldom. The genus Ustilago, on the other hand, shows a difference in the mode of 

 germination. Ustilago Tragopogonis (Fig. 53, B] developes in germination a promy- 

 celium which is divided by transverse septa. The sporidia are formed on the cells of 

 the promycelium and conjugate in pairs. The promycelium of U. longissima (Fig. 53, 

 A] is a narrow cylindrical tube, from the apex of which a sporidium is abjuncted which 

 varies in shape from fusiform to cylindrical. The spores of U. Carbo (Fig. 53, C), on 

 the other hand, put out a short cylindrical tube, which forms sporidia either at the 

 extremities of small lateral branchlets, or by dividing by transverse septa into 

 cylindrical cells. When the spores are being formed the mycelium gives off an 

 unusually large number of branches, which become divided by transverse walls into 

 many cells, and each of these cells is separated eventually from the rest and becomes a 

 spore. The spores are formed in huge numbers, the part of the plant in which this 

 takes place being much deformed and swollen, and the black spore-dust taking the 



^***** 



FIG. 53. Germination of resting-spores of Ustilago. A Ustilago longissima Tul. magnified nearly 700 times. 

 B Ustilago Tragopogonis, magn. 390 times. C Ustilago Carbo Tul, magn. over 390 times; / the promycelium, 

 s sporidia. After De Bary. 



place of the whole of the inner tissue ; plants of maize attacked by Ustilago Maidis 

 show these effects in the most conspicuous manner. U. Carbo produces the * Smut ' 

 of various grasses, as oats and barley. 



Woronin has recently given an account of the development of Tuber cinia Trientalis, 

 an interesting species which is parasitic on Trientalis europaea. In this case also the 

 mycelium spreads through the intercellular spaces, but it possesses organs of suction 

 (haustorid) which penetrate into the cells and there ramify. Tubercinia produces 

 gonidia as well as resting-spores, and multiplies largely by their means. The 

 gonidiophores appear as a cottony covering on the underside of the leaves in spring. 

 The threads of the mycelium all develope towards the underside of the leaf and send 

 out branches at right angles to its surface, which pass through the stomata or between 

 the cells of the epidermis and project beyond the surface of the leaf. These branches 

 either become gonidiophores at once or they spread over the surface of the leaf and put 

 out branches which become gonidiophores. A pear-shaped gonidium is formed at the 

 extremity of the gonidiophore, and when this drops off, another is formed, and then 

 another, till the protoplasm of the gonidiophore is all used up. The gonidia put out 

 germ-tubes in water, and these either form secondary gonidia by abjunction or make 

 their way at once into a leaf of Trientalis. In three weeks at most after the sowing of 

 the gonidia on a healthy leaf of Trientalis black spots appear on it, indicating the 

 presence of resting-spores. These resting-spores are collected into a roundish cluster, 



