604 



COMPARATIVE MORPHOLOGY OF FUNGI 



indefinite in length and cell numbers. Under suitable conditions, copu- 

 lation takes place through copulation tubes, whereupon their cells 

 become binucleate and grow further by sprouting (Brefeld, 1883; Para- 

 vicini, 1917; Bauch, 1923). In the variety macrospora, meiosis occurs in 

 the smut spore; the first sprout cell contains two nuclei of different sexual 

 tendencies which generally are separated by a septum (Fig. 398, 9). 

 The sprout cells arising from these are uninucleate (Fig. 398, 10 and 11) 

 and copulate normally later (Bauch, 1923). 



Tilletiaceae. — In Tilletia Tritici (Dastur, 1921; Rawitscher, 1922) 

 meiosis takes place in the smut spore, as in U. longissima var. macrospora, 

 and proceeds very rapidly, but not quite simultaneously. Generally 

 there are three steps of division, forming eight daughter nuclei in the smut 



spore (Fig. 399, 1 to 7). Frequently 

 some nuclei divide still further, 

 whereby are formed from ten to six- 

 teen nuclei. The nuclei first lie to- 

 gether in a sphere in the center of 

 the cell and migrate into the pro- 

 mycelium which has been formed in 

 the meantime. This is aseptate and 

 on germination in damp earth is, 

 very short; in a nutrient solution, it 

 develops to a long thread whose base 

 emits its protoplasm into the grow- 

 ing tip and remains empty (Fig. 399, 

 8); thereupon the empty parts are 

 successively separated by septa. 

 When the promycelium reaches the 

 surface, a number of acicular sporidia 

 corresponding to the nuclear number 

 are cut off at the tip. Each spor- 



Fig. 399.— Tilletia Tritici. Germination idium contains a nucleus which sub- 

 of smut spores. (i, 6, 7, io x 660; 2 to sequently is separated by a septum 



5 X 1,000; 8, 9 X 500; after Rawitscher, /T? . onf . ft > -ittu-i iu * - ii 



1922, andParavicini, 1917.) ( Fl S- 399 > 9 )- While they still are 



attached to the promycelium or after 

 they have fallen away, they copulate by tubes and the nucleus and 

 cytoplasm of one migrates into the other. The sporidia which have 

 become binucleate develop by conjugate division of their nuclei to slender 

 mycelia which cut off large, thin-walled, binucleate, falcate conidia (Fig. 

 399, 10). These may again develop mycelia which finally penetrate into 

 the delicate tissue of the seedling. 



The remaining forms of the Tilletiaceae correspond with the above 

 picture of germination. In Tuburcinia Trientalis (Fig. 400, 7 to 11), 

 the terminal cells of the promycelium fall away from the germ tube and 



