Permeability 5 
somes in Trianea are usually intensively stained, while those of Sapro- 
legnia and Momordica remain uncoloured. 
This method has been much used to obtain information in regard 
to the mechanism of absorption and permeability, as, for example, 
by Overton (1899, 1900) who concluded that those dyes are absorbed 
by the cell which are soluble in lipoid substances, and Ruhland 
(1908 a } b, 1909 a) who at one time held that the uptake or non¬ 
uptake of a dye by living cells depends on whether the dye is basic 
or acid 1 respectively. This view was combated by Hober (1909) who 
had shown that a number of acid dyes were capable of staining the 
epithelial cells of the kidney. Ruhland supposed that the cell might 
be permeable to the acid dyes but that they combined with no cell 
constituent and so were not accumulated in the cell and consequently 
did not stain it sufficiently for the dye to be visible. The recent work 
of Collander (1921) indicates however that certain sulphonic acid 
dyes examined by him do not enter a variety of plant cells to any ap¬ 
preciable extent. Thus most cells placed in solutions of cyanol extra, 
orange G, methyl orange, Ponceau R and wool violet S for 24 hours 
or more became coloured with the dye to only -J to of the depth 
of colour of the external solution, while analysis of the external solu¬ 
tion showed that this was the true explanation and that the dye was 
not absorbed and so not accumulated in the cell as a colourless com¬ 
pound of dye with a cell constituent. 
Certain cells, however, were shown by Collander to be capable of 
accumulating these sulphonic acid dyes. Such are the cells surround¬ 
ing the vascular bundles of the perianth leaves of a white flowering 
variety of Hyacinthus orientalis, and similar cells in a white flowered 
variety of Tulipa Gesneriana, a fact discovered by Rohde (1917). 
A variant of the method was introduced by Kiister (1911), who 
investigated the absorption of dyes from the cut surfaces of shoots 
or other organs immersed in a solution of dye. He found that a num¬ 
ber of acid dyes were capable of passing into and staining cells when 
introduced to the cells in this manner. This conclusion was confirmed 
by Ruhland (1912 a, b) who also found that out of 30 basic dyes 
tested several were not absorbed by the bulb scales of the onion, 
namely, Victoria blue 4R and B, Basler blue R and BB, gallamin 
1 A basic dye is one in which the radicle to which the colour is due is a base. 
Thus Bismarck brown is the colour base triamidoazobenzene 
NH 2 C 6 H 4 N: NC 6 H 3 (NH 2 ) 2 ; 
it is generally used as the hydrochloride. Similarly, in an acid dye the radicle 
to which the colour is due is an acid. Congo-red is such a case, in which the dye 
as used is generally the sodium salt of the acid. 
