318 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
widely separated due to the expansion of parenchymatous cells surrounding 
them. 
Lenticels. As a result of the expansion of the epidermis, the stomatal 
openings are pulled apart, resulting in the formation of distinct pores or 
lenticels. During the fore part of the season (August 20) they are com¬ 
paratively small in size and conspicuously deep (fig. 8). Cork cells are then 
distributed largely around the edges of lenticels. As the season progresses, 
the lenticels gradually become larger and shallower and more cork cells 
are laid down at the bottom. The fruit developing still further, lenticels 
eventually become flat, shallow openings surrounded and underlain with 
cork tissues. Extreme expansion and mass formation of corky tissues may 
eventually disfigure a lenticel, leaving only a patch of corky tissues with a 
marginal scar of the epidermal cells surrounding it (fig. 9). 
The seasonal changes in relative distribution of lenticels may be of 
interest. A large number of close determinations showed that the average 
number of lenticels per square centimeter of surface area of the fruit had 
decreased between August 20 and September 14 from 44 to 32. 
Table 7. Number of Lenticels per Square Centimeter of Surface of Fruit 
Date 
August 21 September 14 
No. of determinations.13 9 
No. of lenticels.44 32 
Cortex. The pressure test involves primarily the cortical cells. Hence, 
from the point of view of physical changes in the pear the cortical region is 
of far greater importance than any other heretofore considered. Moreover, 
the tissues of the cortex constitute the main edible part of the fruit. Nat¬ 
urally any alterations that may take place here will at once affect its keeping 
and eating qualities. The cells of this part of the pear are extremely thin- 
walled, more or less nearly isodiametric in form, and quite variable in size 
(fig. 10). While arranged rather compactly early in the season, they become 
separated at maturity of the fruit, giving rise to the large intercellular 
spaces. During the enlargement of the pear, cortical cells undergo a rapid 
increase in size. 
Table 8. Measurements of Cells of Cortex (approximately 3-6 mm. below epidermis) 
Ave. Diam., 
Tangential 
Ave. Diam., 
Radial 
Approx. Area 
Long. Sect. 
Increase 
No. of determinations-. . . . 
80 
80 
August 20. 
90 - 5 M 
130.8 [X 
1188 sq. ix 
September 17. 
128.8 u 
178.8 IX 
2301 sq. ix 
93 - 7 % 
Groups of stone cells of considerable size are found scattered throughout 
