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r909] BORDNER—INFLUENCE OF TRACTION ON STEMS 259 
paper and checking off each element by marking through the lumen 
on the yellow paper underneath. 
Method 5.—The hard bast elements were drawn by means of a 
camera lucida and then counted to determine whether an increase 
had resulted in response to the pull. 
Method 6.—Radial and tangential microtome sections of acid- 
fixed material were made to determine whether any fibrous paren- 
chyma existed directly around the hard bast areas. This method was 
used only on control stems of Helianthus annuus. It was the purpose 
to determine whether the elements which produced the increased 
number of bast fibers were present before the tension was applied and 
therefore only developed, or whether they were formed de novo in 
response to tension. 
The plants investigated were Helianthus annuus, Phaseolus vul- 
garis, Ricinus communis, Sinapis alba, Vicia Faba, Lupinus albus, 
Rubus occidentalis, and Vinca major. 
Experiments 
Experiment 1. Helianthus annuus, greenhouse culture.—Ten 
vigorous plants were selected from a number of seedlings grown in pots 
20°" in diameter. The experiment began November 21, 1906, when 
they were mostly ro to rs°™ in height, and ended 29 days later. The 
tension fastening was placed on the experimental plants just below 
the second pair of leaves. The controls were not supported. The 
pull applied to the experimental plants was gradually increased from 
25%™ at the start to 300" on December 14, 1906. The slow growth 
of these plants may be due to the fact that during the entire experi- 
mental period there were only a few sunny days, and also to the short- 
hess of the day at this season of the year. 
_ Table I gives all the data from this experiment, except the follow- 
ing: By method 6, fibrous parenchyma was found in the control stems 
as a transitional form between the thick-walled hard bast fibers and 
the short-celled parenchymatous tissue. These longitudinal sections 
vere taken from just above the cotyledons. The increased number 
of bast fibers in the experimental plants, therefore, may be accounted 
lor as the result of the response of these fibrous cells to tension, which 
thus develop into hard bast fibers. ee Hace 
