Measurement of Rate of Shrinkage of Turgid Tissues. I. 301 
The osmotic pressure of the cell-sap of dandelion scapes was found to 
vary with the advance of the flowering season, being isotonic with a solu- 
tion of 0-42 grm. M. at the beginning (i. e. early April in 1915), and with 
a solution of 0-53 grm. M. at the end (i. e. late June) : this represents a vary- 
ing pressure of about 9 to 11 atmospheres. During the final experiments 
on this material, which were made in the latter part of June, the contractions 
given by the 0*3 grm. M. solution were reduced to only 8 or 10 divisions, and 
in order to obtain one of the high temperature results it was necessary 
to increase the strength of the sugar to 0-40 grm. M., when a contraction of 
23 divisions was obtained at a temperature of 42° C. 
Dandelion Plasmolybic Contraction % at 19 ° C. 
Fig. 13. Curves showing percentage contraction of dandelions at iq° C. with subtonic solution 
(0-3 grm. M. sugar). Ordinates are percentages of total contraction. 
As before, a number of experiments were made at each tempera- 
ture, and the most typical curve selected to represent each temperature. 
As a rule the separate individual curves fell very close together when plotted 
to ordinates of percentage contraction. In Fig. 13 is illustrated the greatest 
divergence found for any one temperature. In this set are however included 
curves from material previously long irrigated with distilled water as well as 
those for short soaking in tap-water. From such a set, the curve A from 
material soaked two hours in tap-water was selected as the one falling with 
the simplest logarithmic regularity throughout. 
