1894.] Growth of Stems in Thickness. 115 
figures show the greatest tension when the temperature was 
the lowest at 2 A. M., while the tension is lowest at I P. M. 
when the temperature was 2° short of the highest point it 
had attained in two days. 
Millardet? hasverified the statements of Kraus with respect 
to the periodicity of tensions, working with Mimosa pudica, 
but he has found that a rise of temperature increases the 
tension, while a fall of temperature diminishes it. Kraus’ 
measurements were made upon stems of trees (maple, birch, 
and oak) that would not show the effect of temperature 
readily, while Millardet’s were made upon the stem, petiole, 
and leaf of a plant that would easily show small differences of 
tension. The subject of tension in tissues is very important 
as each separate tissue has its own rate of growth, causing 
tensions to be set up in the various tissues. In measuring 
stems one has to determine whether an increase in the thick- 
hess 1S temporary, and due ouly to tension, or a permanent 
increase due to growth. If it be tension only, a decrease 
- thickness will follow the increase, this being caused by a 
Contraction of the tissues. 
CORR used for the following work were tomatoes and 
leagth i . being good growers in thickness as well as 
stiff are sd internodes smooth, or at least free from 
to allow of ; fi point had to be looked after carefully so as 
Mies. adjustment of the instrument. While the 
sel vies « were being made, a registering thermometer 
December ong the instrument. The work was done during 
few sunny Pi January, 1892-3, and while there were but 
nee ae ‘caged the plants were under favorable conditions 
and but slight r a goa from the plants would be low, 
the erin: eae of growth from light could occur; 
Would be jn the also, for the most part, was as high as it 
ina steam-heat warmer months, the work having been done 
T ed greenhouse. 
eto 
record Bh. Was measured first, and on Dec. 28th and 29th the 
. n bo : 
Very low, cr Cases of less diameter, the temperature was 
os ch might have occasioned a low tension. 
Mardet 
tes Mouvement nei recherches sur la periodicité de la tension: étude sur 
iques et paratoniques de la sensitive, 18 
