THE EFFECT OF LONGITUDINAL, COMPRESSION UPON 
THE PRODUCTION OF MECHANICAL TISSUE 
IN STEMS 
L. H. PENNINGTON 
(WITH TWO FIGURES) 
Introduction 
For more than a century observations and experiments have been 
made to determine what factors cause or influence the production 
of mechanical tissue in plants. Previous to PFEFFER’s time, the 
causes were supposed to be of a mechanical nature. These expla- 
nations have been shown to be inadequate.' PFEFFER (26, 27) 
showed that tension, pressure, or even contact may act as a stimulus 
to cause the production of more mechanical tissue. NEWCOMBE 
(21) suggested that plants must respond to stress in a self-regula- 
tory manner by producing mechanical tissue where it is most needed. 
He also indicated the complex notion in regard to stress, and sug- 
gested that it should be subdivided. At present wé use the terms 
tension or traction, and pressure or compression, to indicate two 
Opposite kinds of stress 
To determine the effect of each kind of stress, much careful © 
experimentation is necessary. HEGLER (12), BAL (1), HIBBARD 
(14), and BorDNER (2) have investigated the influence of tension 
upon growing cells, with regard to its mechanical as well as to 
its stimulatory effects. Although these investigators did not 
agree in all points, their results show that tension alone cannot 
cause a very marked increase in mechanical strength. VOCHTING 
(34), Hipparp (14), and Bicuer (4) have contributed a little 
concerning the effects of longitudinal compression. 
V6cuTING reported that he fastened weights upon the tops of 
Sunflower stems, some of which had been decapitated, and upon 
Savoy cabbages, all of which had been decapitated. After leaving 
the plants thus weighted for several months, he was able to discover 
* For historical account see UrspRUNG, Biol. Centralbl. 1906. 
Botanical Gazette, vol. 50] [257 
