On the Course of Absorption and the Position of 
_ * 
Equilibrium in the Intake of Dyes by Discs of Plant 
Tissue. 
BY 
GLADYS M. REDFERN, M.Sc., 
University College , Reading. 
With eight Figures in the Text. 
Introduction. 
T HE problem of the absorption of dyes by plant tissue has been the 
subject of much investigation, especially of late years, but few quanti- 
tative data are available. One of the first investigators to examine the 
problem was Pfeffer (4), whose researches established the fact that many 
dyes, especially those known as ‘ intra-vitam stains are absorbed from very 
dilute solutions by plant tissue and accumulate in the cells, either as 
a soluble compound in the cell sap, or as a solid precipitate ; various sub- 
stances in the living cell render the accumulation of the dye possible, the 
best known being tannin and phloroglucin, which form ‘ non-diosmosing ’ 
compounds with the dyes. Pfeffer also demonstrated the fact that normal 
growth continues provided that the external solution is sufficiently dilute. 
Later workers confirmed many of Pfeffer’s conclusions, and established 
the fact that a larger proportion of dye is absorbed from more dilute solu- 
tions. The explanation which was usually accepted was that the dye 
diffused through the ‘ plasma membrane ’ by a process of osmosis, and that 
the concentration gradient was maintained by the formation of non-dios- 
mosing compounds, as described by Pfeffer. 
Recently, however, Moore and his co-workers (3) have challenged the 
theory that the entrance of substances into the cell can be explained as 
a process of osmotic diffusion through a semi-permeable membrane ; they 
explain the powers of selective absorption shown by the cell by the suppo- 
sition that ‘ the cell protoplasm has selective adsorptive powers for different 
ions, and that such ions exist in the cell in combination or adsorption with 
the cell substance ’. 
Stiles and Kidd (6), in experiments on the influence of external concen- 
[ Annals of Botany, Vol. XXXVI. No. CXLIV. October, 1922.] 
