Feb. 28,1916 
Relation of Stomatal Movement to Infection 
1019 
The results (Table V and fig. 1) show that the widths of the stomatal 
pores on cotyledons and mature leaves were greater than those on the 
heart leaves. In general, the stomata on the cotyledons and the lower 
surface of the mature leaves remained open throughout the day, while 
those on the heart leaves were entirely closed at 3 p. m. Those on the 
upper surface of the mature leaves showed a tendency to close from 
11 a. m. to 1 p. m., and then to reopen before their final closure at 6 p. m. 
Shreve (8) found the stomata of Parkinsonia microphylla to exhibit this 
same tendency, since they closed partly during midday and reopened 
again during the afternoon. The stomata on the old leaves exhibited 
only slight movement and that on the upper leaf surface from 9 to 11 
a. m. Readings were not made early enough in the day to determine 
the time of initial opening, but the curves indicate that the stomata on 
the heart leaves opened later than those on the mature leaves and 
cotyledons. This is shown in figure 1, in that at 8 a. m. the stomatal 
pore width on the heart leaves was very much less than on the mature 
leaves and cotyledons, being not more than 2ju on the heart leaves as 
compared to about 9on the others. On cotyledons the stomatal 
openings on the upper and the lower leaf surfaces remained quite com¬ 
parable throughout the day. On the mature and heart leaves, however, 
the stomata of the lower surfaces exceeded in width of pores those of the 
upper surface. This relation was found to occur almost constantly 
throughout the day. In all cases the stomata on the upper surfaces 
closed at about the same time as those on the lower surfaces. 
Table V. —Effect of leaf maturity on average stomatal pore widths on the upper and 
lower leaf surfaces of the sugar beet. Readings 1 were taken at Madison , Wis., on July 
6, 1914. The number of readings made per leaf is given in parentheses following each 
average 
1 These leaves were used for the readings given in Tables I, II, and III, and each leaf has the same number 
in all the tables. 
