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Journal of Agricultural Research yoi. xxvii, no. 6 
may produce abundant germ tubes which form appressoria over the 
stomata and yet do not enter. In these cases it is possible that the 
stomata may not have opened at all. 
It appears probable that entrance in itself, so far as greenhouse studies 
are concerned, is a factor in the resistance of most wheat varieties only 
when the stomatal movement is such as to effect complete closure of 
the aperture. The very fact that many biologic forms regularly enter 
Kanred seedling leaves under greenhouse conditions is sufficient evidence 
that the failure of some forms to produce infection can not be due to 
the small size of the aperture. It seems more probable that the forms 
which do not enter may have a specific physiological effect upon the 
guard cells, which respond by complete closure, or that when entrance 
is effected the germ tubes are destroyed before they can produce any 
easily visible effect upon the host. 
MORPHOLOGY OF THE WHEAT STEM AS RELATED TO RUST RESISTANCE 
During recent years the idea has been prevalent that rust resistance 
was not due to morphology of the host. But it never has actually been 
demonstrated that the morphology of the wheat stem bears no relation 
to the development of Puccinia graminis . On the other hand, there are 
certain suggestions in the early literature that the internal structure of 
the stem may determine in some measure the extent of spread and devel¬ 
opment of the fungus. This is particularly evident in the plates and 
figures by Sappin-Trouffy (47) and Eriksson and Henning {12). 
P. graminis causes the greatest injury when it attacks the portion of the 
stem or peduncle immediately below the rachis, known as the neck. It is 
evident from field observations that the necks of all varieties are not 
uniformly attacked by stem rust. Plate 1, F and G, shows two varieties 
of wheat, one quite susceptible and the other generally resistant to 
stem rust, in the field plots at University Farm, St. Paul. 
The variety shown in Plate 1, F, is Kota, C. I. 5878, which is generally 
considered resistant in the field. It is attacked by stem rust, however, 
and normal linear uredinia are produced. These may be as much as a 
centimeter in length. Usually the uredinia are separate and quite 
distinct to the eye. Even when the infections are numerous, it is not 
difficult to make out the characteristically linear individual uredinia. 
The spores produced are quite normal. 
Plate 1, G, shows the heads and necks of Little Club, C. I. 4066. This 
variety is always very severely rusted at University Farm, St. Paul. 
It sometimes is so severely injured by stem rust that, when heads are 
produced, only very small shriveled kernels are formed. The uredinia 
just below the rachis are very large and confluent. The epidermis 
breaks off as large scales, exposing masses of spores in a single large 
uredinium beneath. 
STRUCTURE OR THE STEM 
In order to study the structure of the stem, several wheat varieties 
were grown in adjacent rows. When the heads were in the soft-dough 
stage, stems were killed and cleared in aceto-alcohol. Sections 10/x 
thick were then cut in pith by means of a sliding razor. Hydrochloric 
acid-orcin, hydrochloric acid-phlorglucin, and analin-sulphate were used 
to differentiate the cellulose and pentosan structures. For permanent 
mounts for photomicrographs, sections were stained with Pianeze stain, 
