USTILAGINALES 



603 



This degeneration goes still further in U. Panici-frumentacei; where 

 the promycelium is no longer four-celled but only two-celled. The distal 

 cell is generally elongated and germinates to a sprout mycelium (Fig. 

 397, 12 and 13). 



In still other species, e.g., Thecaphora deformans on Leguminosae, in 

 U. Vaillantii on Scilla, etc., and U. longissima on Glyceria, no true pro- 

 mycelium is formed. In Thecaphora deformans, the smut spores germi- 

 nate in nutritive solutions to much-branched mycelia which cut off sprout 

 cells (one apiece?) on dichotomous tips. These fall away easily and 

 develop to new mycelia. On germination of the smut spores of U. Vail- 

 lantii in water, there emerge slender, uninucleate, germ tubes which 



\J 



Fig. 398. — Ustilago Vaillantii. 1 to 6. (X 1,300.) Ustilago longissima, var. macrospora 

 7 to 11. Germination of smut spores (X 1,100). (After Paravicini, 1917, and Bauch, 

 1923.) 



grow further. Their fate is unknown. On germination in nutritive 

 solutions the germ tube remains very short and cuts off one or more sprout 

 cells which generally fall away (Fig. 398, 2 to 4). The nucleus divides 

 in three and forms two septa. The three-celled sprout mycelium cuts 

 off at its septa further sprout cells which again become three-celled, etc. 

 In older cultures, copulation takes place (Fig. 398, 5 and 6) either by 

 copulation tubes or between different sprouts or by partial and temporary 

 solution of the wall between two cells of the same sprout. The binucleate 

 cells develop to slender hyphae (Paravicini, 1917). In U. longissima 

 the germ tube develops to a multicellular, uninucleate mycelium which 

 is easily broken up and proceeds to sprouting. The sprouts are again 



