456 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8, 
course of these experiments, Ligowa oats, although heavily infected, pro- 
duced pigment and telia both when growing under normal conditions and 
when subjected to adverse environmental circumstances. (See figure i, 
Plate XXIV.) Avena sterilis L. is considered by Parker as for the most 
part susceptible. In the experiments here reported it produced pigment, 
telia, and extensive hypersensitive areas. Figure 2, Plate XXIV, shows 
leaves of Avena sterilis L. infected by Puccinia coronata Cda. The strain^ 
of rust from Saint Paul, Minnesota, indicated by "S," caused a very light 
infection, the appearance of small scattered uredinia and large hypersensitive 
areas, and the early production of telia. The strain of rust from Tallulah, 
Louisiana, indicated by "T," caused heavy, normal infection without any 
evidence of pigment or telia formation. Swedish Select oats Parker con- 
sidered susceptible, and yet in these experiments Swedish Select oats from 
Virginia produced telia in abundance. Appier oats Parker considered 
resistant. Figure 3, Plate XXIV, shows Appier oats from Alabama infected 
with P, coronata Cda. ''T" shows normal infection with the strain of 
rust from Tallulah, Louisiana; ''S" shows a heavy production of telia and 
extensive dead areas by the Saint Paul, Minnesota, strain. Parker con- 
sidered Burt oats susceptible. In the present experiments Burt oats from 
Alabama showed a similar condition to that described for Appier. 
Therefore, though the production of telia when associated with other 
phenomena indicating resistance may be additional evidence to justify the 
classification of oat varieties as resistant, certainly results obtained in the 
present work seem to show that this phenomenon of telia formation on oat 
seedlings is variable and largely dependent upon environmental factors and 
possibly also upon the strain of rust employed, to such an extent at least 
as to make telia formation a rather unreliable basis for the determination 
of true resistance. 
Summary 
1. Urediniospores borne on the surface of oat seeds do not offer a ready 
means of infecting seedlings developed from these seeds. 
2. Seedlings of oats emerging through soil heavily covered with viable 
urediniospores are not readily infected. 
3. Under Minnesota conditions, a perennial mycelium, capable of 
producing a new crop of urediniospores after overwintering, does not exist. 
What the situation is in the case of wild grasses has not been determined. 
4. Urediniospores do not remain viable over winter on oats, under 
Minnesota conditions, nor does continued production take place. What 
the situation is in regard to wild grasses has not been determined. 
5. Environmental factors influence the development of the rust on oats 
as well as the rate of pustule formation. 
6. Etiolation brings about the early formation of telia on oat seedlings. 
7. Anthocyanin pigment formation surrounding uredinia on infected 
2 The term "strain" is used to indicate merely a locality collection. 
