86 



FIRST GROUP. THALLOPHYTES. 



parenchyma. The pathological appearances produced by them have long been 

 described as Smut or Bunt, and the Ustilagineae themselves are known as Smuts or 

 Bunt-fungi. They sometimes attack their host in certain parts only ; Entyloma for 

 example produces small pustules on the leaves of species of Ranunculus (R. repens} 

 and Calendula ; sometimes they penetrate into the seedling and spread through the 

 whole of the growing plant, and end by forming their resting-spores in special places in 

 the plant. Thus Tilletia Caries forms its spores only in the ovary of the wheat-plant, 

 while the mycelium penetrates through the whole of the plant; Uslilago anther arum 

 forms them in the anthers of the Sileneae, and U. Carbo in the inflorescences of 

 various grasses. The resting-spores form in most cases a black dust, produced 

 oftentimes in considerable quantity in parts of the host which swell with the disease ; 



this may be well seen in Zea Mais when attacked 

 by U. Maidis. The phenomena in the germina- 

 tion of the resting-spores will be described under 

 the several genera. Besides the resting-spores 

 some forms (Tuber cinia. some species of Enty- 

 loma] have also gonidia formed by abjunction on 

 gonidiophores which project above the surface 

 of the host. 



FIG. 52. 



spores, p the promycelium, j sporidia (commence- 

 ment of the formation of sporidia at a), s' secondary 

 gonidium, x a delicate germ-tube from a primary spori- 

 dium. Magnified 460 times. After Tulasue. 



The species of Entyloma appear as parasites 

 on Calendula officinalis, Ranunculus repens, &c. ; 

 spots and weals on the parts attacked show the 

 presence of the parasite. Trie slender colourless 

 hyphae with a few delicate transverse septa grow 

 in the intercellular spaces of the host. Single cells 

 intercalated in the hyphae swell into a spherical 

 shape and become resting-spores, which ultimately 

 fill the intercellular space with their thick masses ; 

 their cell-wall is differentiated into layers (epispo- 



Tillettz Cartes, germination of the resting- . . . 



rium and endospormm). The germination of the 

 resting-spores of Entyloma (e.g. E. Calendulae} 

 agrees entirely with that of the spores of the follow- 

 ing species. 



The rest of the Ustilagineae differ from Entyloma as regards their vegetation in not 

 attacking small portions only of the plant, but in spreading through it ; they enter the 

 plant at its earliest stage and their mycelium grows as it grows. The genera Tilletia, 

 Urocystis, and Uslilago are suitable examples. Fig. 52 shows the germination of the 

 spore of Tilletia Caries. The spore has put out a short blunt germ-tube of limited 

 growth, the promycelium. A whorl of thin pointed branches, the sporidia, is formed at 

 its apex. Before the sporidia drop off from the promycelium, they conjugate in pairs 

 by means of a protuberance (Fig. 52, b}. The sporidia thus united in pairs, put out 

 a germ-tube (Fig. 52, /), which forces its way into the host, or becomes club-shaped at 

 its extremity and gives off a secondary sporidium by abjunction (Fig. 52, /), which then 

 forms a germ-tube to penetrate into the host. Tilletia Caries causes the disease in 

 wheat known as ' Bunt.' The germ-tubes penetrate into the young wheat-plant and 

 grow up with it. The mycelium is at first very inconspicuous and consists of thin 

 delicate filaments ; when it reaches the inflorescence it ramifies copiously, makes its way 

 into the blossoms, and takes possession of every part up to the wall of the ovary. It is 

 in the flowers only that the resting-spores are formed, one on the end of each branch of 

 the mycelium ; the exosporium has reticulate thickenings in T. Caries, while it is smooth 



