June, 1923] 
MURNEEK-CHANGES IN BARTLETT PEARS 
319 
this region. They are surrounded by radially arranged, distinctly elongated 
paranchymatous cells (fig. 11). There is considerable variation in the number 
and distribution of these groups in the various specimens. As the cells of 
the cortex enlarge, the groups of stone cells in a given area become fewer. 
The wound caused by the pressure test being of such a character as to 
tear the cells across their walls instead of separating them from one another 
along the middle lamellae, any change in the walls becomes of prime im¬ 
portance in these considerations. Measurements showed a general decrease 
of close to 15% in thickness of walls of the cortical cells during the harvesting 
season. It is certain, however, that, in addition to changes in thickness, 
Table 9. Measurements of Cell Walls of Cortex (approximately 3-6 mm. below epidermis ) 
Date 
Aug. 2 
Aug. 30 
Decrease 
No. of determinations. 
45 
45 
Thickness. 
1.15 n 
0.98 fX 
14.8% 
other physical and chemical modifications of the cell walls take place at this 
time. Most probably changes in the pectic compounds are of prime im¬ 
portance in this respect. Since no tests were made, one can only conjecture 
what some of these differences may be. 
Vascular bundles. The vascular system being made up of more lignified 
cells than any other tissues considered here (7, 13), one would expect it to 
undergo the least change during the time in question. No study was made 
of seasonal modifications in vascular bundles. 
Fig. 2. Radial sections from the cortex stained with potassium iodid to show distri¬ 
bution of starch: a, 32 lbs. pressure; b, 34 lbs. pressure. Camera lucida drawings. X 25. 
