198 The Botanical Gazette. [May, 
In the third place when tension is induced within tissues a 
thickening of the cell-membrane follows.1* This is shown 
slightly in some plants in which the cortical cells elongate 
toward the center of the stem after the application of a cast. 
It is still more apparent when within a cast a few cells of the 
cortex die and the neighboring cells crowd in to fill the 
space. It is shown also in all my preparations at the limits 
of the casts where great tension has arisen between the con- 
fined segment of stem and that portion just outside the cast 
that is striving to expand.1% All these cases, however, lie 
outside the question as discussed by Wortmann. 
If now we return to the particular case of Phaseolus multi- 
florus, each of several individuals has shown that the per- 
ipheral cell-walls are much thickened where the coils of the 
twine bandage have caused distortion. In this plant also 
there are large intercellular spaces in the cortex at a very 
early age even before the elongation of the hypocotyl is com- 
pleted. The bandage of twine or gypsum causes these inter- 
cellular spaces to be closed within a few days and as a result 
there is at the angles of the cells a double thickness of wall, 
merely an apparent thickening. There was only one case 0 
which there seemed to be a possibility that the cortical cells 
had abnormally increased in thickness of membrane within 
the cast. Here these cells had elongated considerably 
toward the center of the stem, and if the membranes ss 
slightly stronger the change would probably be accounte 
for by the tension called forth. But in this plant it a 
al 
certain that the membranes had so thickened; since 
were no thicker than sometimes found in very young norm 
individuals. It can at least be said that Phaseolus multiflorus 
furnishes no illustration of Wortmann’s theory that membranes 
increase in thickness more than normally when 
. . - 
tension is prevented by mechanical means. All o thee 
used in my experiments have contributed to an gouge 4 
clusion. Moreover, Pfeffer, in his experiments vi ithin 
and stems of seedlings, noticed no unusual thickening W 
the segments enclosed in gypsum. 
The outer pith-cells in many of the species rec 
article become normally thick-walled to such an 
orded in this 
extent that 
ap lischaft det 
'*Hegler’s work as reported by Pfeffer, Berichte d. * a] tissue: 
Wissensch., demonstrates the fact that tension increa i 
*8 For details in these experiments see Newcombe: The € 
resistance on the growth of plant tissues. Leipzig, 1893. 
