Feb. 28,1916 
Relation of Stomatal Movement to Infection 
1037 
reach the pore opening. The reaction upon penetration induces a great 
change in the type of fungous growth, the fungous cells becoming large 
and round. It is to be* concluded that since growth continues imme¬ 
diately in the air chamber below the stomata, the stumatal function 
of gaseous interchange is needed for the development of the mycelium 
in the host, as well as a force for initial penetration. It seems evident, 
therefore, that since germ-tube penetration may occur only when the 
stomata are open, and since stomatal movement is directly related to 
daylight hours, infection takes place only at t this time. 
SUMMARY 
The study of the relation of stomatal movement to infection of the 
sugar-beet plant by Cercospora beticola Sacc. has revealed that certain 
morphological and environmental factors influence stomatal activity, and, 
in turn, the latter, together with a favorable growth of the fungus, influ¬ 
ences infection. 
Leaf maturity, light, temperature, and relative humidity are factors 
concerned with stomatal movement. 
Leaf maturity may be determined by two characters which for any 
given stage have been found to remain uniform—i. e., the number of 
stomata present per square millimeter of leaf surface, and the length of 
the stomatal pore. These characters, taken together, give a good indi¬ 
cation of leaf maturity, regardless of leaf size or position on the plant 
Leaf maturity has a direct relation to stomatal activity in that move¬ 
ment is greater on mature than on young leaves, while on old leaves 
only very slight movement has been observed. 
Light is probably one of the fundamental environmental factors that 
influence stomatal movement, and while direct sunlight may have an 
accelerating action, it is not essential for stomatal opening, since stomata 
may open widely in the shade. 
Good stomatal opening has been obtained at temperatures ranging 
from 70° to 90° F. With these optimum temperatures active, relative 
humidity, with its associated causes and their effects, greatly influences 
stomatal movement. A high humidity favors stomatal opening, while a 
low humidity is associated with closure of the stomata. If the humidity 
remains above 60 through the day hours, the stomata will probably 
remain well open; but if it falls much below 50, stomatal closure will 
probably result. 
Some of the factors influencing infection of beet leaves by C. beticola 
are rapidity of germ-tube growth, maturity of the leaves, and stomatal 
movement. 
Fresh viable conidia of C. beticola germinate equally well and grow 
rapidly in distilled water, soil decoction, irrigation water, and bean 
decoction, in either darkness or diffused light at 24 0 C. 
