274 RESEARCHES ON FUNGI 



ation. The experiment was carried out twice, each time in 

 duplicate. 



When, after the promycelia were well grown, the Petri dishes 

 were examined, it was observed that, in general, the promycelia 

 were not directed toward the source of light, or away from it, or 

 transversely to it, but that their axes were set at various angles to 

 the incident rays. Hence it may be concluded that the promycelia 

 of Tilletia tritici are not heliotropic. 



To determine whether or not the promycelia are geotropic, some 

 chlamydospores were sown on 2 per cent, plain agar in two Petri 

 dishes, and the dishes were fixed in such a position that the surface 

 of the agar was in a vertical plane. One of the dishes was exposed 

 to diffuse daylight and the other kept in complete darkness. The 

 chlamydospores germinated and, 5-6 days after they were sown, 

 the direction of growth of the promycelia was determined with the 

 microscope. The experiment was made on three separate occasions. 



An examination of the plates showed that the promycelia had 

 grown in all directions over the vertical surface of the agar and, 

 therefore, that they had not been influenced in their direction of 

 growth by gravity. Sartoris * states that promycelia developed on 

 the surface of the primary leaf-sheath of a wheat seedling always 

 grow upwards, and he came to the conclusion that the promycelia 

 are negatively geotropic. However, the critical experiments just 

 described do not confirm his deduction. It may be safely concluded 

 that the promycelia of Tilletia tritici are ageotropic. 



Chlamydospores were sown on 2 per cent, plain agar in Petri 

 dishes, and the dishes were fixed in such a way that in some of 

 them the surface of the agar was vertical, as in the preceding experi- 

 ment, in others the surface of the agar looked directly upwards, and 

 in yet others the surface of the agar looked directly downwards. 

 In all the plates promycelia developed in the course of a few days. 

 Invariably it was found that the ends of the promycelia and the 

 tufts of sterigmata were directed away from the agar surface 

 (c/. Fig. 114, A, p. 232). It appears from these observations that 

 the promycelia of Tilletia tritici are negatively hydrotropic. 



1 G. B. Sartoris, " Studies in the Life History and Physiology of Certain Smuts," 

 Amer. Journ. Bot., Vol. XT, 1924, p. 621. 



