136 
JOHN GRAY AND GEORGE J. PEIRCE 
Temperature and humidity readings for each examination of the stomata 
were made. The latter readings were on a Mason hygrometer, which 
consists of a wet and dry bulb thermometer and is supplied with tables 
indicating the humidity at the different readings. Soil samples were taken 
from each box of plants, weighed, dried to constant weight, and the percen- 
tage of soil moisture was calculated from these figures. Darwin and Lloyd 
appear to have worked with mature plants and to have had them under 
fairly constant conditions. We have used the domestic grains, wheat 
{Triticiim vulgare Vill.), oats {Avena saliva L.), rye (Secale cereale L.), 
barley (Hordeum sativum Jess.) ; and the wild oats of this region (Avena 
fatua L.). Plants of each species have been studied under three sets of soil 
conditions, namely (i) with the soil moist, (2) with soil saturated by water- 
ing, and (3) with the soil dry and often caked. They have all been examined 
under such different atmospheric conditions as hot, bright days, cloudy and 
very dark days, and days of light rain. Young, mature, and older plants 
have been studied, each being subjected to the same environmental factors 
whenever that was possible. The degree of illumination and the percentage 
of soil moisture have been recorded for each reading. Most of the expe- 
riments were conducted in a greenhouse with frosted roof but clear end. 
Sunlight is reduced, but only slightly, by these means which, in our climate, 
are indispensable. As a check upon this work in the greenhouse, we cul- 
tivated the same domestic grains in the Experimental Garden, and examined 
them there, under conditions as nearly as possible like those of the green- 
house. The wild oats were studied in the field and also in the greenhouse, 
into which plants of various ages had been removed from time to time in 
order to permit them to adjust themselves to the new conditions. 
These four grains react similarly under like conditions; but each species 
displays individual differences which may be distinguished, and which 
partly explain the differences in needs and behavior which are farhiliar to 
the practical farmer. We shall discuss these differences after each species 
has been reported upon. Barley, wheat, and oats live under conditions of 
soil and of moisture essentially similar, while rye is best grown in drier and 
warmer localities. When planted in a fairly humid greenhouse it presents 
a somewhat different appearance from the normal and from that of the 
other grains. These things are indicated by the details which follow. 
Barley 
Figure i indicates the behavior of stomata of barley seedlings eighteen 
days old and grown in the greenhouse. The soil was very wet in the early 
morning, and no more water was added during the readings. The tem- 
perature was fairly high, but increased, with the increase in light, to a maxi- 
mum qf 34.5° C. at I P.M. The humidity reached its lowest point at 3:20 
P.M., when it was 33%. The stomata opened gradually in the morning 
until 11:50 A.M., when they reached their maximum width for the day. 
