June, 1923 ] 
MURNEEK — CHANGES IN BARTLETT PEARS 
323. 
2. A physical test has been perfected which shows that alterations in 
the structural part of the fruit are evidently more uniformly consistent than 
the chemical changes. 
3. The results of several thousand tests with Bartlett pears showed a 
close correlation between physical resistance to a definite pressure or wound¬ 
ing of the epidermis and cortex, and the maturity of the fruit. When 
measured and expressed in convenient units, the average seasonal decrement 
in this respect was found to be approximately 10 lbs., or close to | lb. for 
every 24 hours. 
4. Though chemical modifications of the cell walls may be responsible to 
a large extent for these differences, the following seasonal morphological 
and histological changes were observed in the Bartlett pear: 
a. There was an average increase of 93.7 percent in size and an average 
decrease of 14.8 percent in thickness of walls of cells of the cortex. 
b. Cells of the lower portion of the subepidermis increased in size (area 
of a longitudinal section) by 65.6 percent, while those of the first layer 
beneath the epidermis increased by 39.3 percent. 
c. Though comparatively slight, still there was a seasonal enlargement 
in size of epidermal cells amounting to close to 14 percent. The cuticle 
covering these cells decreased in thickness at the same time by 19 percent. 
d. The average increase in number of “window cells” per “mother cell” 
was from 2.92 to 4.00. 
e. Lenticels decreased during this period from 44 to 32 per square 
centimeter of surface area of the pear. A conspicuous alteration in form 
and structure of lenticels was noted. 
/. The volume occupied by starch in an average cortex cell decreased 
from 5.49 percent to 1.17 percent. 
5. A partial explanation of the significance of these morphological 
changes and their possible correlation with the physical resistance to pressure 
of the tissues involved is offered. 
The writer wishes to express his sincere appreciation to Prof. E. M. 
Harvey for assistance with the histological work and for many helpful 
suggestions. 
Oregon Agricultural College, 
Corvallis, Oregon 
LITERATURE CITED 
1. Dunbar, P. B., and Bigelow, W. D. The acid content of fruits (Abstr.). Science, 
n. ser. 38: 639-640. 1913. 
2. Ewert, R. Die korrelativen Einfliisse des Kerns beim Reifeprozess der Friichte. 
Landw. Jahrb. 39: 471-486. Pis. 12, 13. 1910. 
3. Farmer, J. B. Contributions to the morphology and physiology of pulpy fruits. 
Annals Bot. 3: 393-413. Pis. 25, 26. 1889. 
4. Hawkins, L. A., and Sando, C. E. Effect of temperature on the resistance to wounding of 
certain small fruits and cherries. U. S. Dept. Agr. Bull. 830, pp. 1-6, fig. 1. 1920. 
