Eric Drabble and Hilda Lake. 
190 
a cover glass. Under a tf-in. objective the effect on the cells was 
readily observable. The solution which just failed to plasmolyse 
was taken as isotonic with the cell sap. Thus, if ’13 plasmolysed 
the cells while ‘12 did not, then - 12 was taken as the strength of 
the sap. The most convenient plants for these determinations 
proved to be those with a red colouring matter in the epidermis, 
since in these the first appearance of plasmolysis was readily seen. 
Experiment has shown that but little difference in the strength of 
sap obtains between the red and colourless cells from the epidermis 
of the same leaf. 
Some of the results are given below:— 
Plant. 
Locality and Conditions. 
Strength 
of Sap in 
Gram 
Mols. of 
N. & Cl. 
Taraxacum Dens- 
leonis 
Damp grass at side by ditch, near 
Thames, at Kew 
•11 
Elodea canadensis ... 
College fresh-water tank 
•12 
Saxifraga 
sarmentosa 
Cool House, Chelsea Physic Gar¬ 
dens 
•13 
Spiraea sp. 
Shrubbery in Sir Joseph Hooker’s 
garden, at Sunningdale 
•13 
Mahonia sp. 
Ditto ditto 
•13 
Geranium 
Rohertiauum 
Northfleet, near, but not in, salt 
marsh 
•17 
Ditto ... 
On rocks above Cwm Idwal, near 
Twll Du 
•23 
Hieracium sp. 
Ditto ditto 
00 
O'! 
Vaccinium myrtillus 
Ditto ditto 
•28 
From this series it is evident that a greater concentration of 
cell sap occurred in those plants which had been most strongly 
subjected to factors tending to promote loss of water by transpira¬ 
tion. Taraxacum growing in long grass by a fresh-water ditch. 
Elodea completely submerged in fresh-water, Spiraea, and Mahonia 
in a shrubbery, showed comparatively low osmotic equivalents. In 
