Measurement of Rate of Shrinkage of Turgid Tissues. I. 293 
was never found in any abundance except in the endodermis. In an old 
scape bearing the nearly ripened fruits, no starch at all could be detected 
except in the endodermis in the uppermost region of the scape. There 
is a ring of vascular bundles embedded in the ground tissue, and laticiferous 
elements occur in the pericycle, but no interfascicular cambium develops, 
and for the purposes of this research these tissues can be disregarded. 
Thin strips of turgid dandelion scapes show well-marked tissue tensions. 
By the method of de Vries the mean isosmotic strength of the cell-sap was 
found to be equivalent to a solution of 0*43 grm. M. cane-sugar at the 
beginning of the flowering season (April in 1915), and 0-53 at the end (late 
June). This was confirmed by microscopic observation, but no exact 
measurement of single cells was made as for the onion. 
Section V. Choice of a Solution for investigating 
Rate of Plasmolytic Shrinkage. 
For the plasmolysing solution it is desirable to use one which neither 
injures nor penetrates the protoplast. The solution which has most 
frequently been used is cane-sugar, which fulfils both these conditions more 
or less satisfactorily, and can be obtained readily in a pure form. 
The choice of a suitable concentration is a matter of more difficulty. 
The simplest course seemed to be to find the isosmotic equivalent of the 
cell-sap and to use a solution which was j ust hypertonic to this. By 
examining thin strips of dandelion scapes and onion leaves after the manner 
of de Vries, it was found that a sugar solution of 0-5 grm. M. was j ust hyper- 
tonic to the cell-sap of the dandelion, and 0-3 grm. M. was hypertonic to 
that of the onion. These solutions were first used for the various tempera- 
tures, but owing to the difficulty of deciding when the contractions had 
ended, and to the variable forms of the curves obtained, both stronger 
and weaker solutions were subsequently experimented with. The solutions 
thus investigated were respectively 0-731, 1 * 0-5, 0-3, and 0-18 grm. M., all being 
made up to * weight-normal 5 standards. The whole contraction produced 
by these solutions was measured by a microscope on a micrometer screw 
travelling horizontally, as well as by the optical lever apparatus, and was 
found to vafy somewhat with the age of the material, but approximate 
values are given in Table I. 
Sugar 
solution. 
0-18 grm. M. 
0-30 grm. M. 
0-731 grm. M. 
Table I. 
Dandelion. 
Contraction % C ontradion of 
{scale divisions'). original length. 
15-40 c* 2-0-4 % 
2CC-25O 2-2*5 % 
Onion. 
Contraction 
{scale divisions'). 
20-50 
200-350 
% Contraction of 
original length. 
°- 3-°\5 % 
1 This strong solution (25 %) was largely used by van Rysselberghe 
X 
3 % 
