Aug. 15, 1914 
Head Smut of Sorghum and Maize 
365 
Since none of these methods can be presumed to correspond closely 
to the natural process of infection, the conclusions drawn from them 
must be largely a matter of inference. The small number of plants and 
the abnormal conditions in the greenhouse make it unnecessary to con¬ 
sider method bn(x), in plat B, Nos. 1 and 2, further than to note that 
both seeds and soil were heavily inoculated and that the seeds were germi¬ 
nating. Moreover, method bmx in the same series (plat B, Nos. 3 and 4) 
produced 100 per cent of infection on six plants, so that both these 
methods appear to have been proportionately more successful than 
elsewhere, probably because of the more thorough technique where so 
few plants were concerned. It appears, indeed, that the abundance 
of infectious material provided has been the most salient factor involved. 
Without it at Amarillo natural infections were often so numerous that 
the effect of inoculation was not perceptible; compare, for instance, 
plat A, No. 7, with plat A, Nos. 9 and 13, and plat A, No. 8, with plat A, 
Nos. 10 and 14. Method amx, which is closely similar to bmx on account 
of the large amount of spore material provided, the seedling having to 
grow up through the latter in both cases, has also produced a compara¬ 
tively large percentage of infection, even exceeding bmx (plat E, No. 3) 
at St. Paul. 
These results immediately suggest that no such crucial period for infec¬ 
tion of the seedling obtains in the case of this smut as has been observed 
by Brefeld (1895, p. 46) for Ustilago cruenta , for the presence of the infect¬ 
ing organism during the whole of the early development of the host pro¬ 
duces the disease when its presence on the seed alone will rarely do so. 
While £/. cruenta was not able to infect, in Brefeld’s experiments, after 
the leaf sheath had been split as far down as 1 cm. from the tip, the 
plumules of the plants inoculated by method bm(y)—a dusting of dry 
spores over the seedlings—in plat E, No. 8, averaged close to 2.5 cm. in 
length and yet were nearly as abundantly infected as those which were 
smaller and more heavily inoculated four days before (plat E, No. 3). 
The difference between the* latter and plat E, No. 4 (method amx) is 
not sufficient to militate against the conclusion that a late period of infec¬ 
tion is possible, although it has seemed from the character of the infection 
in the mature plant, as revealed by the histological studies already dis¬ 
cussed, that the infection in the field at Amarillo is usually quite early in 
its origin. That it is systemic in the individual culm more character¬ 
istically than in the plant as a whole, however, supports this idea of late 
infection (see p. 348). Investigation has shown, moreover, that the 
hyphae were at least not widely disseminated in the growing tissues of 
several seedlings which later developed infection. In the seasons of 
1910 1 and 1911 about 200 seedlings at three to four weeks after planting 
were dissected and a part of the meristem—that containing the primary 
1 The dissections in this season were made by Mr. V. X,. Cory. 
