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Igto] PENNINGTON—LONGITUDINAL COMPRESSION 265 
respectively. Careful microscopic examinations and measurements 
failed to show any differences in cells or cell walls. 
POPLAR (ONE-YEAR-OLD PLANTS) 
Sixteen plants of the poplar were selected and placed under 
experimental conditions in April. The plants were measured and 
carefully tied to stakes. Weights were suspended upon eight of the 
plants, and as the plants increased in size more weights were added. 
Although growth practically ceased in early summer, the plants 
were kept under experimental conditions until October. 
The final measurements and tests showed no greater increase 
in the experimental plants than in the control plants; the increase, 
in fact, was somewhat less for the former than for the latter. For 
the experimental plants, the increase in height. and diameter of 
the stem was less than 16 per cent, and for the controls 20 per cent; 
the relative increase in xylem 77 and too respectively; the resist- 
ance to bending 81 and 100 respectively. It is difficult to account 
for these differences. Although the conditions for growth were not 
good, owing to partial defoliation by insects, they were the same 
for both experimental and control plants. 
CASTOR OIL PLANT (GREENHOUSE PLANTS) 
Twenty-four plants of the castor oil plant were selected from a 
large number which were grown in the greenhouse. Before tying 
the plants to the stakes, the stems were carefully protected with 
pieces of table matting. Internodes of bamboo, about 10 cm. in 
length, were split in two and the halves bound upon opposite sides 
of each stem, the lower ends extending to within 5 cm. of the ground. 
Weights were suspended from the upper ends of these pieces of 
bamboo. In this way room was made for the weights to swing 
free from the ground, and the longitudinal pressure was confined 
to the lower 5 cm. of the stems. The plants were kept under 
€xperimental conditions for four weeks. The stems were 6 mm. 
in diameter and 15 cm. high at the beginning of the experiment; 
they increased about 50 per cent in diameter and 70 per cent in 
height during the experimental period. At the conclusion of the 
experiment, the experimental stems were under a pressure of 
about 1000 grams, equivalent to about 1.33 atmospheres. 
