43 ° 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
promycelium but elongate to form the so-called infection threads (PI. 
2, F a, H d). Frequently not all of the sporidia elongate (PI. 2, F b), 
but eventually appear to lose their protoplasm and become hyaline. 
Fusion of these elongated sporidia and also the production of secondary 
sporidia (PI. 2, I a) were observed in a very few cases, though in the great 
majority of instances they merely became elongated. The size and 
length of the promycelia, sporidia, and infection threads varied with the 
conditions of germination. 
SPORE GERMINATION 
The spores of Urocystis tritici do not germinate readily or consistently 
in either distilled or tap water. With spores from material about a 
month old and kept seven days on soil, McAlpine (9) secured limited 
germination in a water culture after 24 hours incubation. Approxi¬ 
mately 40 per cent of the spores of the previous season germinated after 
being floated on tap water for about four days. 
Various solutions and media were tried under different conditions of 
moisture and temperature by the writer, but though the spores free from 
any leaf tissue would germinate under one set of conditions at one time, 
they would not germinate under apparently similar conditions at another. 
Thus many negative results were obtained. It may be of interest to 
note those conditions under which fairly high percentages of germina¬ 
tion were secured. In 1920 a method was found which since then has 
given fairly high and uniform results. In these studies spore-laden 
leaves were powdered and used as a fine dust-like mixture instead of 
using spores free from leaf tissue. This material was floated on dis¬ 
tilled water in a Syracuse watch glass and placed at 18 0 to 20° C. Some 
spores germinated at the end of two and three days, although the best 
germination usually was had on the fourth day. The germination, once 
started, proceeded very rapidly, and the elongated sporidia, or infection 
threads, were quite numerous on the fifth day. 
Good germination was secured many times in 1921 in tap-water cul¬ 
tures after two to five days incubation. The spores free from leaf tissue, 
however, did not germinate readily in distilled water, though a few spores 
sometimes germinated after four or five days. The optimum tempera¬ 
ture for germination was 18 0 to 20° C., though germination at 25 0 was 
recorded in one culture and in certain others at 12 0 to 13 0 . Satisfactory 
germination was obtained at io° after seven to eight days when spores 
mixed with pulverized leaf tissue were used. However, in infection 
experiments herein described no infection was obtained at 25°, though it 
did occur at 6° to 12 0 . 
In December, 1921, fairly good germination took place after three to 
four days in juice expressed from wheat seedlings and diluted. In some 
instances germinating seeds were found to stimulate spore germination. 
In October, 1921, spores which had been dusted on seeds which were 
placed on soil in a Petri dish in the laboratory germinated freely after 
two days, while spores from the same source dusted on soil and on the 
surface of both tap water and a soil solution, did not germinate after 
four days of incubation. 
During the course of these experiments this stimulating effect of 
germinating seeds on spore germination was observed also in some tests 
of the viability of spores buried in the soil. For these experiments 14 
samples of spores which had been buried under different conditions were 
