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AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
the cortex. They are roundish-polygonal, very thick, and are layered and 
dotted with many pore canals. Radially arranged parenchymatous cells 
adjoin groups of stone cells. 
The structural features of the epidermis are described in further detail by 
Zschokke (19). Increase of the surface of the fruit is accomplished partly 
by subdivision and partly by expansion of the epidermal cells. Tangential 
walls of the epidermis become thickened early in the development of the pear. 
Great differences in amount of cuticle were observed between fruit grown in 
the sun and that grown in the shade. The “bloom” consists of particles 
of wax. Stomata are present in all young fruit. As the fruit grows, they 
disappear or are torn and become lenticels. Morphologically, the sub¬ 
epidermis differs considerably from that of the cortex. The cells are smaller, 
more tabular, thick-walled, and contain tannin and pigment bodies. Color 
of fruit depends on the contents of these cells. Within the subepidermis 
are found scattered stone or grit cells. They are plated on the outside and 
pointed toward the core. This layer of stone cells is present in all pears. 
In some it forms almost a “stony shell” all over the fruit. 
It is to be noted that none of the above-named investigators take 
cognizance of such morphological or physical alterations in the pear as may 
be exhibited comparatively late in the development of the fruit and may 
therefore be coincident with the time of harvesting and marketing of the 
crop. No correlation is noted between the morphological features and the 
condition of maturity of the pear. 
A Physical Test for Maturity 
In view of the existing situation, the Oregon Agricultural Experiment 
Station has for the past four seasons endeavored to find a simple but reliable 
test for maturity of pears. As the work progressed, it was soon evident 
that such a test, in order to be applicable, must be based largely, if not 
entirely, upon the physical properties of cells rather than upon their chemical 
contents. Of the various new testing methods under consideration, a simple 
one, since then known as the “pressure test,” has given strikingly satis¬ 
factory results. Work extending through four seasons has shown that it 
is by far the most practical means of measuring the changes in maturity of 
pears (10, 14). 
This new test is based upon the fact that during the growth and ripening 
of the pear there is a gradual and consistent alteration in physical resistance 
to pressure or wounding of the epidermal and cortical regions of the fruit. 
On the average this amounts to close to one half pound every 24 hours. It 
points either to rapid changes in size or to some other modifications of the 
structural parts of the cells. A special apparatus was constructed for the 
purpose of measuring and expressing in convenient units this change. 2 
2 For a description of the apparatus and of its use, see Oregon Agricultural Experiment 
Station Bulletin 186, pp. 7-10. 
