320 
AMERICAN JOURNAL OF BOTANY 
[Vol. 10 , 
Cell contents: Starch. Of the various substances found within the cell, 
solids only are of importance in this study, since they only would have any 
bearing upon a physical test of this nature. Besides protoplasm and some 
minor substances, starch is the usual important solid in the cells of the 
cortical region of the pear. During the early part of the development of 
the fruit there is an abundance of starch in all tissues excepting the con¬ 
ducting vessels (text fig. 2, a). As the fruit matures starch disappears 
rapidly, the disappearance beginning with the region near the primary 
vascular bundles and thence continuing through the cortex to the periphery 
of the fruit. The final traces of starch are usually visible in the subepi- 
dermal region (text fig. 2, h). On August 20, starch grains, 6-11 microns 
in diameter and spherical or nearly so in form, were found either singly or 
in aggregate groups of several grains in almost all cells (text fig. 3, a). 
Fig. 3. Cells of Bartlett pears showing relative amounts and distribution of starch: 
a, Aug. 20; b, Sept. 17. Camera lucida drawings from one optical plane, more than one 
cell in thickness. X 200. 
Actual counts and measurements of starch grains as found early and late in 
the season, 6-8 mm. below the epidermis, showed that the approximate 
calculated volume occupied by starch diminished from 5.49 percent to 1.17 
percent (text fig. 3, h). 
Table 10. Number and Size of Starch Grains in Cells of Cortex 
(1 approximately 6-8 mm. below epidermis) 
Ave. No. of 
Grains per 
Cell 
Ave. Diam. 
of Grains 
Percentage of 
Volume Occupied 
by Starch 
No. of determinations. 
10 
3 i 
August 20. 
54 
8.7 n 
5-49 
September 17. 
36 
7.8 IX 
1.17 
