Feb. 9, 1924 
Resistance of Wheat to Puccinia graminis tritici 387 
15 difference in the number of stomata on the different 
^ El T- a / S haS the , least - and KhapK consistently the most, 
(table III.) The difference in the number of stomata on these varieties 
^ems unrelated to the degree of resistance to stem rust in the greenhouse. 
Khaph, the most resistant wheat used for determining biologic forms 
of rust at University Farm, has the largest number of stomata. What 
appears to be more pertinent to the problem is the frequency and the 
extent to which the stomata open. ' 
Size and Movement op Stomata 
Allen (1) suggested that the inability of many germ tubes to gain 
entrance into Kanred wheat might be due to the size and shape of the 
stomatal aperture. r 
The writer compared the size of the aperture of stomata of five Wheat 
varieties. The method employed by Lloyd (30) was used. Epidermis 
strips were placed immediately into absolute alcohol, and then studied 
under the microscope. Check observations were made by fastening 
growing leaves to the substage of the microscope and observing the 
stomata direct. Measurements made in this manner agreed entirely 
with those from epidermis strips placed in alcohol. 
It is obvious from these observations that the stomatal slits of Kanred 
wheat are open to a much greater extent than would be expected from 
AHen s preliminary report. These data are shown in Table IV. 
Allen (r) found that only about io per cent of the germ tubes of a 
lorm from which Kanred is immune entered this variety, while about 
30 per cent of the germ tubes of a form to which Kanred is susceptible 
entered. The following explanation was offered: “The presence of the 
appressonum might act as a stimulus by mere contact, by altering the 
gaseous exchange through the stoma or disturbing the moisture relations 
by exerting a possible toxic influence upon the guard cells, or bv its 
presence shutting off some of the light from the guard cells. It is at least 
conceivable that the guard cells might be sensitive to the appressorium 
and remain closed, thus excluding the fungus.” She also observed that 
m Baart, a variety very susceptible to most biologic forms of P 
grammis tritici, only 67 per cent of the germ tubes which formed appres- 
sona entered. ^ 
Newton (j 7 ) has studied the behavior on Kanred of the germ tubes of a 
biologic form which fails to produce pustules or flecks on this wheat 
variety) and concludes that approximately 30 per cent of the germ tubes 
which form appressoria enter. This difference in the observations of 
different investigators strongly suggests that conditions during the 
incubation period influence the number of entries which the fungus is 
able to make. It seems probable, therefore, that the conditions which 
influence the opening of the stomata, both before and after appressoria 
are iormed, may have considerable effect on entrance. 
Loftfield (31) points out that the stomata of cereals rarely are all open 
i°i^i Clr at same time. Even under the most favorable 
neld conditions all the stomata are open only for one or two hours each 
day the tendency in cereals being to operate with many closed stomata. 
He further observed that on many days the stomata of wheat plants do 
not open at all. 
On die two days prior to the date of observations, careful examination 
showed that the stomata of the six wheat varieties used in the experiment 
