INFLUENCE OF LIGHT UPON ACTION OF STOMATA 
examined on days with high clouds, or with Hght rain, the soil moisture 
being about the same as before, namely 12%, showed that the stomata 
remained open throughout the day. In this respect there was more variety 
of action among the older plants than among the younger ones. Thus 
figure 17 records the behavior of two such plants, a young, 4-8 inches high, 
and b a plant in bloom, under the same conditions and on the same day. 
The temperature reached 34° C. at 1:40 P.M., and the humidity remained 
almost constant, namely at about 60%. There was no direct sunlight during 
the day, but at times there were very bright intervals. Wild oats, therefore, 
are able to absorb CO2 and to manufacture food on days when the other 
plants here reported upon would keep their stomata closed, because the 
stimulus required for their opening would be too weak to produce the needed 
effect. On the other hand, figure 16 indicates the behavior of a mature 
wild oat plant growing out of doors in the Experimental Garden. After a 
day of rain the moisture in the soil amounted to 12%, the sky was cloudless, 
and the sunshine correspondingly bright. Nevertheless, the stomata 
closed at the time of maximum illumination. This time was also that of 
maximum temperature and minimum humidity. Apparently we have, in 
this behavior of the wild oat out of doors, a decided contrast with the be- 
havior of the cultivated grains. Its behavior in the greenhouse is similar, 
however, to the others. Out of doors the conditions of its existence are 
somewhat different from those ordinarily prevailing for the cultivated 
varieties, as the following description will show. The wild oat of California 
grows and fruits throughout most of the year, naturally reaching its best 
development during the wet weather of early winter and of spring. The 
leaves are slender, tough, thick, and hairy, well adapted to withstand 
severe drying of the soil; for this species grows commonly along dry road- 
sides and in open fields and pastures, where it is subjected to pronounced 
drying, perhaps more than once during its life. The specimens which we 
studied were well developed and in bloom during the early part of December. 
In midsummer and later the plant would not thrive, and only where there 
was some moisture would it hold out at all. On the' other hand, the culti- 
vated grains can be grown at any time of the year, providing there is suffi- 
cient warmth, moisture, and light. They are naturally spring species, 
however, and grow best with the warm rains, and fruit in the early summer. 
In these differences in habitats, and in the corresponding differences in 
habits, we see reasons for the behavior of the two sets of plants. 
That the behavior of Avena fatua, in the respects in which it differs 
from that of the four cultivated grain plants which we studied, is the 
product of circumstances is indicated by figure 18, in w^hich the move- 
ments of the stomata of wild and cultivated oat plants are recorded. In 
this experiment in which wild oats, transplanted from a field and kept 
in the greenhouse for thirty-five days, were compared with cultivated 
oats, we find the following circumstances. The temperature was moderate 
