454 ; BOTANICAL GAZETTE [JUNE * 
; Historical 
The first observations to determine the effect of strain upon 
the plant were by Knicur (12) in 1803, when he allowed fruit 
trees to sway in the wind in one plane only and obtained a greater 
increase in wood on the two sides in the direction of swaying; 
this he considered to be due to a greater movement of sap through 
a loosening of the cells, a merely mechanical process. 
In 1879 BARANETSKY (2), investigating the periodicity of 
growth, found that when a small amount of tension (10-30 grams) 
was applied to a stem, it had the effect of retarding the growth | 
in length. 
ScHoitz (21) confirmed these observations, but found that 
two results were produced: first an acceleration and later a retarda- 
tion of growth; the first result he attributes to a rapid growth of 
the cell-membrane, the second to a pathological condition in which 
the building up of the materials is hindered. 
HEGLER (8), working along the same lines, found that this 
retardation of growth bears a close relation to the daily periodicity 
in elongation of the stem. This, he says, demonstrates that tension 
calls forth a response in the cell, hence is a true irritation stimulus. 
HEGLER (Q) also investigated the effect of tension upon the 
anatomical structure of stems. By gradually increasing tension 
on seedlings of various plants, he found that the breaking strength 
was in many cases nearly doubled in three days, due to an increase 
in amount of the collenchyma, sclerenchyma, and bast, a much 
greater increase than takes place under normal conditions. 
Batt (1) later repeated HEGLER’s work and found no increase 
in mechanical tissues even in the plants with which HEGLER worked. 
HiBBArD (10), also working along the same lines, found no 
increase in mechanical tissues with tension except in one plant 
(Vinca), where a slight increase was noted. 
The work of V6cuTING. (23) upon Helianthus annuus, of 
WIEDERSHEIM (25) upon woody stems, and of KELLER (11) upon 
fruit stalks has likewise shown no response due to tension. 
Later work by BorRDNER (3) seems to show an actual increase 
in breaking strength and in amount of mechanical tissue in the 
several species with which he worked. This investigator, by the 
