142 
JOHN GRAY AND GEORGE J. PEIRCE 
Open. Hence, the behavior on one day, in one set of conditions, was the 
opposite of the behavior on the following day, under conditions exactly the 
reverse so far as light was concerned but similar in every other respect. 
To answer the question what effect, if any, the conditions in the green- 
house exerted upon the behavior of the stomata of these four species of 
grain plants, we grew another set in the open, in the Experimental Garden 
which now forms part of the equipment of this laboratory. When fifty-five 
days old, on December 29, they were examined. The results are indicated in 
figure 14. The day followed a cold frosty night, but was very clear from 
early dawn. The sun appeared at 8:30 A.M.^ The humidity fell to 57% 
at I :i5 P.M., but it remained much higher during the rest of the day, both 
earlier and later. The temperature was about 15.5° C, ranging somewhat 
above and below this figure. It is obvious too that, at this season of the 
year, even in a latitude no further north, the position of the sun results in a 
light intensity considerably less than at other seasons. Nevertheless, it 
will be seen, on comparing the stomatal curves in this figure, 14, with those 
of the same species previously reported and experimented upon under glass, 
that there was little or no difference in the general behavior of the stomata. 
At 2 P.M. the light began to fade and all the stomata began to close. Of the 
four, the stomata of wheat closed soonest, the other three closing at about 
the same time and rate, as the line Y-Y' shows. These results indicate 
plainly that, so far as stomatal action in response to light is concerned, 
there is little or no difference in behavior due to the effect of the greenhouse. 
Wild Oats 
While the experiments above described were in progress it was suggested 
that we ascertain the behavior of the native wild oats (Avena fatua L.), 
which were growing in the Experimental Garden. Several plants were 
potted and taken into the greenhouse. Figure 15 indicates the stomatal 
movements on a young and on an old plant on the day following trans- 
planting. The soil was kept very moist, and the light was moderately 
bright. The stomata on the young plants remained open during the bright- 
est part of the day, from 9:15 A.M. till 2:05 P-M., but on the old plant they 
failed to open. 
Mature plants of wild oats tend to open their stomata somewhat during 
the early morning hours, and then to close them for the remainder, and the 
hottest part of the day. Figure 16 shows this action on a very clear, 
bright day, with the temperature at 23° C. and the humidity at 43% 
during the middle of the day with the soil moisture at 12%. Similar plants 
1 It should be stated that, owing to the two mountain ranges bounding the Santa Clara 
Valley to the eastward and the westward, sunrise and sunset are respectively later and earlier 
than they would be on a wide plain in the same latitude. Sunset and darkness come espe- 
cially earlier in our laboratories because Stanford University is built at the foot of the hills 
which rise to the mountains to the west. 
