296 



USTILAGINEAE. 



celia, may develop to mycelia; coalescence of conidia is unknown. 

 In nutritive solutions conidia are formed in large numbers, and 

 multiply yeast-like till nutriment fails. 



Ust. succisae Magn.^ frequents the anthers of Scdbiosa Succisa, 

 and forms pure white spores, easily distinguished from those 

 of the two preceding species. The anthers appear to be thickly 

 covered with glassy granules. The spores produce four-eeUed 

 promycelia from which conidia are formed. (Britain.) 



Ust. tragopogonis (Pers.) (Britain). 

 This fungus forms its spores in flowers 

 of species of Tragopogon, and in many 

 localities has a wide distribution. 

 The development of the flower is 

 retarded, so that it retains externally 

 the appearance of a flower-bud en- 

 closed in its bracts (Fig. 161). The 

 dark- brown or violet spores escape 

 through intervals between the bracts ; 

 they are 13-17At long, 10-15^ broad, 

 with reticulate markings on their 

 coats. They easily produce in water 

 four or five- celled promycelia from 

 which conidia are given off, often 

 followed by coalescence. In nutritive 

 solutions development is much more 

 vigorous, secondary conidia may be 

 produced, and coalescence always takes place. 



Ust. scorzonerae (Alb. et Schwein.) is at first sight very 

 similar to Ust. tragopogonis. Its spores are found in flowers 

 of Scorzonera humUis, Se. purpurea, and cultivated species, e.g. 

 Sc. hispanica; while its mycelium hibernates in the perennial 

 root-stocks of these. The spores are produced rapidly and 

 in large numbers ; they germinate easily in water, forming a 

 four-celled promycelium, and thereafter conidia which do not 

 pair. 



Ust. cardui Fisch. v. "Waldh. (Britain). This is the cause 



of a stunting of the flower-heads of Carduus acantJwides, C. 



nutans, and Silylmm, Marianum, while at the same time they 



become filled with a brownish-violet spore-powder. The spores 



' Magnus, Hedwigia, 1875. 



Fig. 162. — Ustilago tragopogonis. 

 Development of spores : successive 

 stages of development, ill order of 

 the letters, a, Sporogenous branch, 

 just appearing on the surface of 

 young corolla of Tragopogon pra- 

 tensis, and beginning to form a tuft 

 of branchlets. b and c, Formation of 

 spores from the mycelium, d, Spore- 

 clump with several ripe spores, the 

 episporium of wliich is coloured 

 dark-violet and thickened in a 

 reticulate manner, (x 300). (After 

 De Bary.) 



