Lioyp: LEAF WATER IN GOSSYPIUM 3 
calculated to 100 square centimeters of leaf blade. In this way 
the changes in dry weight and in leaf water for each period were 
determined. 
STOMATA. The measurements given in TABLE IX are average 
micrometer measurements of a large number of stomata for each 
period, made on material fixed in absolute alcohol.* Those in 
TABLE X are measurements of living stomata made in the field 
by the following method, first hit upon by me during my work at 
the botanical laboratory of the Carnegie Institution of Washington, 
at Carmel, California, during the summer of IgII. 
A microscope, provided with a condenser and a 4 mm. objec- 
tive with long working distance, was provided with a cooling cell. 
This was extemporized by wiring a Soyka flask beneath the sub- 
stage apparatus. For working in the field, a heavy camera tripod 
served as a stand capable of ready adjustment in height and 
position. The illumination consisted of direct sunlight, or when 
that was not available, a strong artificial light. I used a small 
miner’s acetylene lamp, on the whole fairly satisfactory. A small 
arc light probably would be better, and indeed necessary when 
the leaves are very thick. 
By means of such strong illumination, properly centered and 
controlled with the iris diaphragm, it is possible to measure 
accurately living stomata of leaves with a thickness of 5 mm. 
without at all injuring them. The method is adapted to the 
observation of the stomata on a great variety of leaves, including 
many which are densely covered with trichomes (e. g., Parthenium 
argentatum Gray; Chenopodium sp.), which being out of focus 
do not interfere with the vision under strong illumination. The 
stomata at the bottom of deep pits, such as are found in the 
Cactaceae, also can be seen, but so far this has involved the 
removal of a thick slice of the underlying tissues. 
The method presents the further advantage, one of great 
* importance in field work, of permitting the repeated observation 
of the living stomata, or indeed of a single one, during a sustained 
period, without injury to the leaf or its removal from the plant. 
This method has, of course, its limitations in view of the size and 
*Lloyd, F.E. The physiology of stomata. Carnegie Inst. Wash. Publ. 82. 1908. 
