600 



COMPARATIVE MORPHOLOGY OF FUNGI 



and terminal growth, these spores develop indefinitely into easily dissoci- 

 able sprout mycelia (Fig. 395, 4, 8 and 9), with slightly ellipsoidal, uni- 

 nuclear cells, which continue budding until food is exhausted. In U. 

 violacea and Testicularia Cyperi, the whole promycelium may be loosened 

 from the smut spore and, lying free in the nutrient solution, may sprout 

 further. When the food is exhausted, the sprout cells form long fine 



filaments on the surface so that 

 in some forms, as U. zeae (Fig. 

 396, 2 and 3), a white pellicle 

 results (Brefeld, 1895). From a 

 %'i \k& '■^^ definite moment, i.e., at a certain 



ic] ';■/ \ |<2h F&A oxygen tension of the medium 



(Bauch, 1922), the sprout cells 

 copulate either directly or 

 through copulation tubes (Fig. 

 395, 10 and 11). Descendants 

 of the same promycelial cell, at 

 least in Ustilago violacea, do not 

 copulate with each other. The 

 four tetracyte nuclei are sexually 

 differentiated in pairs. Appar- 

 ently each nucleus impresses on 

 its cell a definite sexual character, 

 thus causing the formation of 

 copulation tubes (Kniep, 1919). 

 In the form of U. violacea on 

 Dianthus deltoides, there appear 

 secondary sexual characters 

 which distinguish the sprout 

 mycelia of both sexes by the 

 physiological peculiarities of 

 their behavior toward albu- 

 moses, peptones and disodium 

 phosphate (Bauch, 1922). The 

 sprout cells, which become bi- 

 nucleate, bud further with con- 

 jugate division of their nuclei 

 until they reach a suitable host, 

 within which they form germ tubes and develop to binucleate mycelia 

 which in turn form sori in the "predestined" organs. 



U. Zeae and U. Vuijckii form an important exception to this scheme. 

 Here the sprout cells do not copulate, hence the hyphae within the host 

 are uninucleate and plasmogamy first takes place in the sorus (Rawitscher, 

 1912, denied by Seyfert, 1927). The gelatinous denticulate portions 



Fig. 395. — Ustilago Scabiosae. 1 to 4. Germ- 

 ination of smut spores. Ustilago violacea. 5 to 

 7. Germination of smut spores. 8, 9. Sprout 

 mycelium. 10, 11. Copulation of sprout cells. 

 (1 to 7, 10, 11 X 1,000; 8, 9 X 1,500; after 

 Harper, 1898.) 



