RUST RESISTANCE OF OAT VARIETIES. ■ 7 
On the upper leaf blades of the plants inoculated at the time of 
heading, where one would normally expect the ultimate production 
of telia, the resistant plants seemed to produce them at a remarkably 
early stage. These early telia were produced, in all cases observed, 
only, on leaves infected with the crown rust. It is the belief of the 
writer that such a hastening in the completion of the life cycle of 
the fungus is entirely comparable to the well-known instances in 
the seed plants of the influence of unfavorable conditions, such as 
drought, poor soil, and injury, in hastening the period of blooming 
and the maturing of seed. 
The teliospores are to be considered necessarily as the final stage 
in the year's life cycle of the rust. These spores do not serve to 
spread the infection during the current season, but provide a means 
for the reproduction of the disease another season or when conditions 
are again favorable. 
It may be argued that the ability which the fungus in these par- 
ticular varieties possesses to produce this final spore form is the best 
possible indication of extreme susceptibility. Nevertheless, it is 
certainly true that if a variety is able to prevent the formation of 
the summer-spore stage of the rust, the spread of the disease will be 
checked in localities where only such varieties are grown. 
This unusual occurrence of telia on seedling leaves is thought to be 
an additional evidence of resistance. It has been used sometimes in 
making the distinction between resistant and susceptible individual 
plants. Whether this interpretation is accepted or not, the presence 
of telia on seedling plants of some and their absence on other strains 
grown under identical conditions is very good evidence of real dif- 
ferences in the protoplasmic reaction of the two hosts, for the prog- 
ress of the rust fungus following infection is quite different in the 
two instances. The same stimuli, whether they are chemical, enzymic, 
or osmotic, which cause the formation of flecks in some varieties 
and not in others may exercise a rather direct influence on the ability 
of the parasite to produce a particular spore form at any given time. 
Norton (10) reports the abundant occurrence of aecia of the 
asparagus rust on plants which were resistant to the uredinial stage 
of the rust. 
Smith (11), in studies of the water relations of asparagus rust, has 
found that " a very direct relation exists between atmospheric mois- 
ture and the prevalence of the several spore forms of the rust," and 
that " the teleuto stage may occur in asparagus beds little affected by 
the rust, and apparently not preceded by any trace of the other 
spore stages." He concludes that "the teleuto stage is then to be 
regarded as a provision for surviving any condition unfavorable to 
the fungus, whether of food supply, moisture, temperature, or resist- 
ance by the host, without regard to season." 
