THE EFFECT OF TENSION UPON THE DEVELOP- 
MENT OF MECHANICAL TISSUES 
OF PLANTS. 
BY 0. M. BALL, PH. I). . 
Professor of Botany and Mycology, Agricultural and Mechanical College of Texas. 
The subject which will be discussed in this paper has been but par- 
tially investigated. 
In 1893; Hegler, 1 an assistant in the laboratories of Dr. William Pfeifer, 
at Leipzig, announced the results of certain experiments from which it 
appeared that when a slight tension is applied in the direction of growth 
to young seedlings such as the field bean and the sunflower, there occurs 
first a diminution in the rate of growth and later an acceleration as 
compared with the normally growing seedling. This matter had already * 
been investigated by Scholz 2 and Baranetzky. 3 
This tension was secured by attaching small weights of 20-30 grams 
to a thread, passing this over a lightly moving roller and making the 
free end fast to the plant under investigation, the whole being placed in 
such position that the tension upon the tissues of the seedling was in 
the direct vertical line. 
This diminution and acceleration of growth was fully confirmed by 
other investigators. It appears that the slight amount of tension pro- 
duced by the weight acts as an irritant, at first checking and then stim- 
ulating growth. Thus far, these effects are analogous to those produced 
by certain other irritants such as, at times, sudden changes in tempera- 
ture, a series of small shocks, or slight wounds, and abrasions of the grow- 
ing parts. 
Hegler investigated the matter further and found that more important 
and far more complicated results could be obtained by applying tension 
in the manner described and increasing the strain at intervals. He 
claimed in this way to be able to develop certain tissues such as the bast 
and collenchyma to such an extent that the tensile strength of the plant 
would be vastly increased, and in fact claimed to be able to develop, 
during the course of a few days, certain mechanical tissues in plants in 
which these do not normally appear, or at least, as has since appeared, 4 
1 Hegler: Cohn’s Beitrag Z. Biol. d. Pfanzen, 1893, Bd. 6, p. 383. 
2 Scholz. Idem., 1887. Bd. 4, p. 323. 
3 Baranetzky Angleiche Periodicitat d. Langen-Wachs Thums, 1879. 
4 Kiister, Flora, 1900, p. 173. Pfeffer, Pflanzen Physiologie. Bd. II, 2 Aufl., 
1901, p.148. 
