Transpiration as a Factor in Crop Production. 191 
two bundles. There is little differentiation in the corn leaf 
between the chlorophyll-bearing cells of the upper and lower 
surface of the leaf. The rather loose texture of the leaf with the 
relatively large air spaces is characteristic of a vertical section in 
this region. Figure 2 is the same kind of a section taken closer 
to the bundle, thru a row of the cells of the chlorophyll-bearing 
bundle-sheath. The texture of the leaf here is not so loose as in 
the region illustrated in the preceding figure. Figure 3 is a longi- 
tudinal view of a leaf thru the vascular bundle. Compact tissue 
relatively free from air spaces is always found in and immediately 
surrounding the bundles. A chlorophyll-bearing sheath of single- 
cell thickness is always a prominent feature in connection with 
a bundle. Figure 4 is a cross section of a leaf showing a single 
bundle. The compact chlorophyll-bearing tissue is here seen in 
cross section. The water-conducting tissue of the bundle is 
represented by three heavy walled tubes shown in cross section. 
The relationship of a stoma in connection with its underlying 
air chamber to the internal leaf tissue is here seen. Figure 5 is a 
cross section of two bundles showing a lateral connection between 
the water conduction elements of the bundles. This doubtless 
accounts for the fact that a bundle in a leaf may be cut without 
completely isolating the remainder of that bundle in respect to 
its water supply. Figure 6 is a cross section of one of the more 
prominent ribs of a corn leaf. The thick-walled protective tissue 
on both the upper and lower sides of the bundle is characteristic. 
Small bundles are completely surrounded by a chlorophyll-bearing 
sheath while large bundles such as this one are only partly en- 
compassed. 
Plate IV has two semidiagrammatic figures. Figure 1 is a 
three-plane view of a corn leaf. The view given here is the same 
as that of three walls of a box. The features shown are the 
same as those already explained in other figures, so that detail 
is not necessary. The three planes have not been drawn in 
perspective but merely assembled to show their relationship. 
Figure 2 is a two-plane view of a portion of stem, showing cross 
and longitudinal sections in their relative positions to each other. 
The longitudinal section view is taken midway between the large 
vascular elements which always show so prominently in any cross 
section view of corn bundles. The phloem seen at d in cross 
section and d in longitudinal section consists of sieve tubes and 
numerous companion cells. This tissue is always located at one 
side of the water-conducting tubes. 
