486 
Journal of Agricultural Research voi. xxvn, No. 7 
12. According to the conditions of the experiment, the spores ger¬ 
minated within a hydrogen-ion range of P H 3.6 to 7.1. Optimum 
germination occurred within the range P H 5.1 to 5.7. 
13. The relative humidity to which the spores are exposed has a 
marked effect on their viability. Relative humidities of from 50 to 75 
per cent were most favorable for retention of viability. Spores kept 
at these humidities within a temperature range of from 5 0 to 26.5° C. 
frequently commenced to germinate shortly after they were placed in 
distilled water, without the addition of a stimulatory agent. 
14. Wheat seedlings in which the coleoptiles were more than 4 mm. 
long did not become infected when they were inoculated with dry spores. 
When seedlings were inoculated with large numbers of dry spores, some¬ 
times no infection occurred, whereas inoculations with few germinating 
spores at suitable temperatures consistently resulted in heavy infections. 
15. Soil temperatures ranging from 14 0 to 21 0 C. were optimum for 
infection of wheat seedlings by Urocystis tritici. The most severe and 
earliest-recorded infection occurred on plants kept at 19 0 to 21 0 . Some 
plants became infected at 23 0 to 25°. No infection occurred at 29 0 to 
31 0 . Inoculation at 15 0 and subsequent transfer of the plants to tem¬ 
peratures above 23 0 resulted in a decrease of the amount of infection. 
Some plants became infected at 5 0 . 
16. Studies of the nuclear phenomena during germination of the spores 
indicate that the spore nucleus divides at germination, the nuclei migrate 
to the promycelium, and usually a single nucleus wanders into each 
sporidium. When the sporidia germinate, this nucleus divides, the germ 
tube becomes binucleate, and this condition may be retained for a con¬ 
siderable period. Germ tubes containing four nuclei were rarely observed. 
Conjugation of sporidia was sometimes observed. A single germ tube 
may be produced from the conjugated sporidia, and this germ tube at 
first contains the two nuclei which migrated from the sporidia. 
17. The mycelium within the plant is typically intercellular, and 
haustorialike bodies are sometimes observed. Branching and fusion of 
the mycelium occur within the plant. Prior to spore formation, 
binucleated hyphal cells were observed. 
18. Although some spores appear to arise from a single hypha, fre¬ 
quently two distinct hyphae appeared to be involved. Sterile cells 
and spores arose simultaneously from single coiled structures, and 
differentiation of the cells occurred as development proceeded. 
19. Infection hyphae of Urocystis tritici were observed to have entered 
the tissues of rye seedlings which are known to be immune from the 
disease. 
LITERATURE CITED 
(1) Anderson, Paul J. 
1914. THE MORPHOLOGY AND LIFE HISTORY OF THE CHESTNUT BLIGHT FUNGUS. 
Bul. Comm. Invest, and Contr. Chestnut Tree Blight Dis. No. 7, 44 p, 
17 pi. Bibliography, p. 37-42. 
(2) Bartlett, H. 
1923. wheat crop competitions, 1922. In Agr. Gaz. N. S. Wales, v. 34. 
P- 15-23. 
(3) Brefeld, Oscar. 
1895. brandpilzE hi. In his Untersuchungen aus dem Gesammtgebiete der 
Mykologie. Heft 12, p. 99-236, pi. 6-12. Munster. Bibliographical 
footnotes. 
(4) BrittlEbank, C. C. 
1920. flag smut. In Jour. Dept. Agr. Victoria, v. 18, p. 240-243, 3 fig. 
