1026 
Journal of Agricultural Research 
Vol. V, No. 22 
Outside in the greenhouse the humidity ranged from 31 to 34 after 11 
a. m., and the stomata were entirely closed at 4.20 p. m. 
A comparison of the stomatal pore widths of the leaves in the green¬ 
house on May 16 with those in the same place on May 17 shows that on the 
former day the stomata were practically closed all day, while on the latter 
they opened early and remained fairly well open till after 2 p. m. The 
humidity on the two days was quite different, being appreciably higher 
on the 17th than on the 16th. This offers an explanation for the differ- 
Fig. 4.—Stomatal pore widths on mature leaves kept under different relative humidities in a humidity box 
(H. B.) and free in the greenhouse (G. H.) at Rocky Ford, Colo., on May 20, 1913 (Table VII). 
ence in stomatal pore opening, though, of course, conditions on the two 
separate days can not be compared too closely. 
In another test, made on May 20, the stomata in the humidity box again 
showed greater widths of pores than those outside in the greenhouse 
(fig- 4) an fi the humidity ranged about 10 units higher throughout the 
day in the former place than in the latter. The greatest difference in the 
stomatal opening in the two places occurred after 11 a. m. when the 
stomata in the humidity box had much greater stomatal pore widths 
than those outside. The humidity remained generally near or above 60 
in the box, while outside it was, on the average, below 50. The initial 
