USTILAGINALES 



601 



of a sporogenous hypha lie beside each other in pairs (Fig. 396, 4 to 9), 

 the separating walls dissolve and nuclei migrate toward the middle, while 

 both sides become thinner and emptier; generally they can still divide 

 into two daughter cells. They then round off, thicken their walls and, 

 with the fusion of the dicaryon, are transformed to smut spores. 



These figures of germination in Figs. 395 and 396 are of the Ustilago 

 Scabiosae type and are extensively modified in many other forms of the 

 Ustilaginaceae. In U. domestica (Fig. 397, 11), on Rumex domesticus, 

 and U. Holostei (Fig. 397, 10), sprout cells are formed only on two pro- 

 mycelial cells, where many are present in whorls. In U. domestica they 



Fig. 396. — Ustilago Zeae. 1. Germinating smut spore. Promycelium, P, developing 

 a sprout mycelium. 2. Sprout mycelium. 3. Hypha with sprout cells. 4. Uninucleate 

 hyphae from a lesion on corn. 5, 6. Uninucleate hyphal cells. 7 to 9. Copulation. 

 10. Young spore. 11. Mature uninucleate spores. (1 to 3 X 300; 4 to 11 X 660; after 

 Brcfeld, 1895, and Rawitscher, 1912.) 



copulate as soon as they have fallen away; in U. Holostei the upper ones 

 grow downwards clinging close to the promycelium, the lower ones grow 

 upwards and copulate without falling off. Only the binucleate sprout 

 cells fall away and germinate to sprout mycelia (Brefeld, 1895). From 

 analogy to U. violacea, we must assume that the promycelial cells are 

 sexually differentiated. 



In Cintractia Montagnei on Rhynchospora, the promycelium is four 

 celled (Fig. 397, 6 and 7), the lower cell generally remaining in the spore 

 (Rawitscher, 1922). Immediately after the formation of septa, or almost 

 simultaneously, each pair of neighboring cells copulates either by resorp- 

 tion of the wall or by copulation tubes; the content of one cell does not 



