8 
Walter Stiles 
dissolved substance into the cells. Again if a cell contains soluble 
calcium salts, the entrance of a soluble carbonate or oxalate will 
result in the formation of a precipitate of the corresponding calcium 
salt. In this manner Pfeffer was able to show the permeability of 
cells to ammonium carbonate. Conversely if a cell contains soluble 
oxalates or carbonates, the permeability of the cell to calcium salts 
can be similarly determined. Osterhout (1910) showed that root 
hairs of very young seedlings of Dianthus barbatus formed crystals 
of calcium oxalate when the roots were in a solution of a calcium salt, 
but not otherwise. The following solutions were used: 0-005 M calcium 
sulphate, 0-005 M calcium nitrate, 0-005 M calcium chloride, 
o-oooi M calcium hydrate, dilute artificial sea water and tap water. 
Crystals of calcium oxalate made their appearance in root hairs of 
Dianthus barbatus within four hours at 30° C. after immersion in the 
solutions, and in the case of calcium sulphate in 1-5 hours. 
The penetration of iron salts into cells rich in tannin is rendered 
visible in the cell by the production of a blue colour. By the use of 
this test Miss Williams (1918 b) was able to show that hypodermal 
cells of the leaf stalks of London pride (Saxifraga umbrosa) are nor¬ 
mally impermeable to ferric chloride, but that after treatment with 
various electrolytes the protoplasm becomes permeable to ferric 
chloride which enters the cells at such a rate as to give a definite blue 
colour within three minutes, whereas before treatment such a colora¬ 
tion is not produced after immersion for two hours in this salt. 
The absorption of copper salts by a tree of Quercus macrocarpa 
was recognised on account of the metallic copper which accumu¬ 
lated in the cells (cf. MacDougal, 1899). Accumulation is made pos¬ 
sible in this case by the reduction of the copper in the penetrating 
salt to metallic copper, so that equilibrium between the copper salt 
inside and outside the cell is not reached and endosmosis of the salt 
therefore continues. 
(iv) Sugars and Glycerol. The penetration of glucose, sucrose and 
glycerol into the cells of water plants such as Lemna, Elodea and 
Potamogeton , Can be demonstrated by the formation of starch from 
the absorbed sugars or glycerol inside the cells (Boehm, 1883; Meyer, 
1886; Acton, 1890). The absorption of the sugar or glycerol takes 
place in the dark, while in control experiments with the same plants 
not provided with sugar or glycerol, no starch is formed. 
Ruhland (1911) used this method to examine the permeability 
of the cells of sugar beet leaves to a variety of sugars. He found that 
raffinose, sucrose, maltose, glucose, fructose, certainly entered the 
