186 BOTANICAL GAZETTE [SEPTEMBER 
were planted under each of two glass cages provided with cotton 
ventilators to prevent the entrance of spores from the air. The 
experiment was afterward repeated in the greenhouse, but rust 
never appeared on the plants in either case. The conditions 
however were exceedingly abnormal. The ventilators were 
entirely too small and the moisture inside the cages was always 
excessive. While the plants grew rapidly, headed, and_blos- 
somed, they failed to set seed both years. Another experiment 
made in the spring of 1905 appeared to give more favorable results. 
Wheat was sowed at various dates, some of it quite late. It was 
all inoculated early and repeatedly with both aecidiospores and 
uredospores of P. graminis tritici Erik. and Henn., the latter being 
obtained chiefly from the experimental plot of winter wheat of 
the same source as noted above, but the wheat of every sowing 
remained nearly free from rust until it began to head, when each 
in turn became thoroughly rusted. It might be assumed on this 
evidence that wheat has only a definitely limited period of sus- 
ceptibility, still very small volunteer wheat plants are often quite 
rusty in the fall. It is possible to attribute this peculiar behavior 
to infection through the seed with a long subsequent incubation 
period in the growing plant, although the possibility of its coming 
through the soil is not excluded. 
The infection of wheat grains with P. graminis can often be 
recognized by the presence of a tiny black spot where the grain 
separated from the mother plant. When black, this area is gen- 
erally filled with teleutospores, which can be distinguished in mass 
with the naked eye or at least with the aid of a hand lens. Such 
grains are usually shrivelled, but occasionally they remain quite 
plump. Grains showing a spot of larger area with somewhat 
irregular boundaries are usually infected with other fungi, as 
Alternaria or Helminthosporium, and may not even contain rust. 
These are the so-called ‘‘black-points”’ mentioned by BoLLEy.‘ 
In rusted grains of wheat the pustules are usually most abun- 
dant in the thick portion that was formerly attached to the rachilla, 
but they are also found in other parts of the pericarp, and often 
lie in the seed coats where they are pressed against the endosperm 
4 Science, Oct. 21, 1910, p. 1. 
