Transpiration as a Factor in Crop Production. 189 
a punch. The fixing agent used was a water solution of 1 per 
cent of chromic acid and \ per cent of acetic acid. The specimens 
were allowed to remain in this solution 24 hours and were then 
washed 24 hours in running water. They were then transferred 
to 15, 35, 50, 70, 80, 95, and 100 per cent alcohol at intervals 
of about 2 hours, then to 25, 50, 75, and 100 per cent xylol at 
the same intervals. After thoro infiltration with paraffin, the 
specimens were imbedded and put away for sectioning. The 
material for stem work was preserved in alcohol and formol in 
the proportion of 95 c. c. of 50 per cent alcohol and 4 or 5 c. c. of 
40 per cent formol. The stomata material was stripped from the 
leaf and plunged at once into 100 per cent alcohol. 
The leaf sections were cut 10 to 15 microns thick and stained 
in safranin and light green. The safranin stain consisted of 
equal parts of a saturated water solution and a saturated alcohol 
solution. 
The light green was a saturated clove oil solution. The stem 
sections were stained in the same safranin and light green. The 
stomata material was stained in Delafield's haematoxylin and 
eosin. The material was mounted in balsam for permanent slides. 
A comparison of fresh material with permanent mounts showed 
very clearly that with the latter the chloroplasts in the cells of 
the chlorophyll-bearing bundle-sheath assumed an abnormal 
elongated shape and grouped themselves in an unnatural crescent 
arrangement about the outer edge of the cells. For this reason 
the chloroplasts have been drawn in these cells in the following 
plates as they occur in fresh material. It is of interest to observe 
the distinct difference in size, and reaction to the killing process, 
between the chloroplasts in the cells of the chlorophyll-bearing 
bundle-sheath, and those of the leaf parenchyma in general. 
All other tissues shown in the camera lucida drawings have been 
checked with fresh material and found to be normal. 1 
TISSUE STRUCTURE. 
Plate I contains microphotographs showing the general charac- 
ter and arrangement of the tissues involved in the transpiration 
current of corn. Figure 1 is a vertical section of the root showing 
the root cap and the origin of the vascular strands. Figure 2 
shows in cross section the specialized area of the corn root thru 
which the water ascends, for the most part, after its intake from 
the surrounding cells. The vascular tissue of the root is arranged 
in one circle around the central portion of the root. The origin 
of a lateral rootlet is seen in the figure. Figure 3 is a 1-5 sector of 
1 The author is indebted to Dr. Florence A. McCormick for suggesting a 
comparison of the fresh and permanently mounted specimens. 
