1909] BORDNER—INFLUENCE OF TRACTION ON STEMS 257 
strip of wood or bamboo about 1oc™ long was placed crosswise 
between the cords coming up on opposite sides of the stem,'to keep 
them from injuring the young leaves and growing tip of the stem. 
In the field cultures, exactly the same methods were followed, 
except that the seeds were planted in rows. The inferior seedlings 
were removed, and only the stronger ones were left for experimental 
use. In most cases the heavy clay loam was sufficiently firm to keep 
the plants from being pulled up by the tension. In the few cases 
when the soil was not firm enough, heavy flat weights were used to 
hold it in place. 
METHODS IN FINAL DETERMINATIONS 
Method 1.—In all but two experiments the stems were tested by 
direct pull along their longitudinal axes to determine whether they 
had responded in a self-regulatory manner to traction by increasing 
their breaking strength. 
Preliminary experiments convinced the writer that the method 
of obtaining the breaking strength used by BALL was not satisfactory, _ 
since too many of the experimental plants broke at or just below 
the tension fastening. Larger plants therefore were used. These 
were broken at some distance below the tension fastening, thus elimi- 
nating the unquestionably weakening effect coming from the pressure 
of a tension fastening on the young and tender stem. 
For this purpose, a strong wooden frame was constructed, about 
t20°™ long and soc™ high. Through the middle of the frame ran 
a shelf parallel with top and bottom. On this shelf rested the plant, 
blocks, and spring balance used in determining the tensile strength. 
To Stasp the ends of the stem, 4 blocks of wood were selected, each 
ing 5°™ thick, ro°™ wide, and 20° long. These blocks were laid 
together in pairs, one block above its mate, and grooves considerably 
larger than the stems were cut in the contact faces of each pair to 
Téceive the plant stem. 
_ During the preliminary experiments, the stems, except in the por- 
ton to be tested, were wrapped in moist cotton and then imbedded 
‘a damp mixture of sand and Portland cement. This mixture 
"as placed in the groove of the lower half of the pair of blocks. The 
stem was then placed in position and more concrete was piled on top. 
