88 
Effect of Tension on Plants. 
which possess these tissues only in traces. For instance, he found that 
a seedling of the sunflower which .at first could support a weight of 
only 160 grams, after having been weighted for two days with 150 grams, 
could support 350 grams. Likewise, petioles of Helleborus niger, which 
at first sustained only 400 grams, would after successively increasing the 
tension for a few days, sustain a weight of 3500 or more grams. These 
astonishing results, if true, would afford a most striking example of the 
power of living organisms to adapt themselves to changes in their environ- 
ments. According to his results, this power of resistance was acquired 
through an increase in the number of the cells in the Collenchyma as 
well as an increase in the thickness of the walls of the collenchyma, 
schlerenchyma and of the hard bast cells, and in the case of Helleborus, 
in the development of an entirely new tissue, namely, hard bast, which 
originated from the phloem elements already present. 
It is well known to all that certain parts of plants are at times sub- 
jected to greater strains than at others. The fruit-stems of apples, of 
gourds, oranges, bananas, and such fruits as increase largely in weight 
while maturing must develop their powers of resistance to the constantly 
increasing strain of the enlarging fruit. The tissues in the limbs of 
fruit trees when fully loaded must be subject to far greater strains than 
during the intervals of fruiting. Boughs of hemlocks, firs and pines of 
northern climates must in winter often sustain for a great length of 
time not only their weight, but an added burden of snow and ice. The 
tendrils of climbing plants are subjected to the constantly increasing 
weight of their parent stems. Evidently there must be a compensating 
increase in the tensile strength of the parts subjected to such increasing 
weights, and certain increases in thickness have been observed in these 
latter cases, although it is still a matter of question how much of this is 
due to tension and how much to contact irritation. 5 
While the element of tension apparently plays a very important part 
in all these cases, it will be observed that the line of action is not the 
same in all. In fruits and in the side limbs of trees, either when sus- 
taining their own ever increasing weight or an added burden of snow or 
ice, the weighting force, acts, in general, in the line of the direction of 
gravitation and hence, is one at all times acting under natural conditions, 
whereas in HegleEs case the force acts directly opposite to gravitation 
and is, moreover, one which, under no conceivable natural condition, 
could occur. Bearing this point in mind we see that two questions are 
to be considered : 
“Worgitzky, Vergleichende Anp.tomie d. Ranken Flora, 1887, p. 69. Von Ders- 
ehan Einfluss v. contact u. Zug auf Rankende Blattstiele, Leipzig, 1893. 
