268 BOTANICAL GAZETTE [OCTOBER 
that no increase in mechanical tissue had been caused by weight 
or compression, cross-sections were prepared and careful examina- 
tion made to determine the relative amounts of collenchyma, 
hard bast, and xylem. In none of these tissues could any difference 
be detected between the experimental and the control plants. 
SUNFLOWER (GARDEN PLANTS) 
Thirty sunflower plants were selected from a large number of 
plants and placed under experimental conditions in June. Longi- 
tudinal compression was confined to the lower part of the stems by 
using pieces of bamboo, as in former experiments. Conditions 
for growth were very favorable. The plants were about 15 cm. in 
height and 6 mm. in diameter at the beginning of the experiment; 
during the experimental period of nine days, they increased 100 per 
cent in height and 70 per cent in diameter. The weights, which 
were necessarily light at first, were increased daily until the average 
weight for each experimental plant was 1400 grams (about three 
atmospheres). 
At the conclusion of the experiment the usual measurements 
and tests, with one exception, were made. Instead of determining 
the resistance to crushing in this series, the tensile breaking- 
strength was determined by means of BoRDNER’s (2) apparatus: 
If we assume that roo represents the value of each measurement 
and test for the control plants, the following numbers represent 
the values of corresponding measurements and tests for the expel 
mental plants: height at the beginning of the experiment 10 5-55 
at the conclusion 110.2; diameter at the beginning 94-1; at ‘the 
conclusion 99.4; resistance to bending 80; _ tensile breaking- 
strength 64.2; amount of xylem 80.4. These numbers show 
that, although the amount of growth in both the experimental 
and control plants was practically equal, the gain in strength and 
in mechanical tissue was less in the former than in the latter. The 
heavy weights evidently retarded the production of mechanical 
tissue. 
A second series of 24 somewhat older sunflower plants was placed 
under experimental conditions in the usual manner by tying the 
