802 
Journal of Agricultural Research 
Vol. XXVII, No. IO 
examination of sections of the leaves showed that the mesophyll cells of 
sorghum leaf are smaller, more numerous, and more compact than those 
of a leaf of corn. In the case of both corn and the sorghums, the amount 
of dry matter in the leaves begins to increase in the morning from 4 to 
6 a. m., reaches a maximum at periods varying from 2 to 6 p. m., and then 
gradually diminishes until daylight the following morning, when the 
amount of dry matter again approximates that at the beginning of the 
previous day. In the three comparative experiments with Pride of Saline 
com and Dwarf Yellow milo, the increase in the amount of dry matter in 
the leaves during the day was always greater for the sorghum than for the 
corn. In each of these three experiments the maximum increase in dry 
matter per square meter of leaf was respectively 4.8, 2.6, and 5.4 gm. for 
the com and 7.6, 10.7, and 10.1 gm. for the milo. If the materials used 
by the leaves in respiration are not considered, the increase in the weight 
of the dry matter of the leaves during any period of the day represents 
the difference between the amount of material manufactured by the 
leaves and the amount of material translocated from them during that 
time. It is not possible, therefore, to state definitely whether the greater 
increase in the dry weight of the leaves of milo as compared to the leaves 
of com is due to a higher rate of production of materials by the leaves of 
sorghums or whether it is the result of a more rapid rate of translocation 
of the manufactured materials from the leaves of com. The fact that the 
sorghums can increase the amount of dry matter in their leaves under 
climatic conditions that have prevented any increase in the amount of 
material in the leaves of com would seem to indicate that the milo under 
the conditions of these experiments is able to manufacture materials in 
the leaves practically twice as rapidly as the corn. 
Under the conditions of these experiments the amount of water in 
any given area of leaf was always lower in the sorghums than in the 
corn. The amount of water in the leaves of both com and the sorghum 
begins to decrease anywhere from midnight to 5 a. m. and reaches a 
minimum from noon until 3 p. m., after which time the amount of water 
begins to increase until it again reaches a maximum the following morn¬ 
ing. In the experiments with the sorghum the minimum amount of 
water in the leaves occurred at 12 noon in four cases and at 1 p. m. in 
two cases. In the four experiments with corn the minimum amount of 
water in the leaves occurred three times at 2 p. m. and once at 3 p. m. 
In only one case did the quantity of water in the leaves appear to be 
the limiting factor in the production of dry matter. In the experiment 
on August 1, 1916, the amount of dry matter in the leaves of com reached 
a maximum at 10 a. m. and remained constant until after 4 p. m., when 
it began to decrease. The amount of water in the leaves at 10 a. m. 
was 112.4 gm. per square meter of leaf, and it continued to decrease until 
it amounted to only 104.2 gm. per square meter of leaf at 2 p. m. In 
none of the other experiments with com did the amount of water in the 
leaves reach a minimum lower than 117 gm. per square meter of leaf. In 
all of the other experiments the amount of dry matter in the leaves of 
corn continued steadily to increase past the time of the minimum water 
content of the leaves, so that it would appear that the minimum amount 
of water that can be reached in the leaves of corn and not interfere 
with the process of photosynthesis is slightly above 112 gm. per square 
meter of leaf. The minimum amount of water observed in the leaves 
of Dwarf Yellow milo and Red Amber sorgo in these experiments was 
98 gm. per square meter of leaf, but this minimum apparently in no 
way retarded the production of dry matter. 
