Permeability 11 
sufficiently long a blue coloration was produced indicative of the fact 
that nitrate had diffused into the cells previously. The result of the 
test was negative if the time of immersion in the nitrate was short. 
The analysis of tissues, expressed sap and extracts of tissues has 
been used considerably as a test of permeability. Thus Nathansohn 
(1903) made analyses of the expressed sap of the marine alga Codium 
after immersion in a solution of sodium nitrate and was in this way 
able to obtain data with regard to the penetration of sodium and 
nitrate ions into this plant. Paine (1911) used the same method to 
investigate the permeability of yeast cells to inorganic salts, and con¬ 
cluded that the slight intake he observed was entirely due to adsorp¬ 
tion of the salt by the cell wall. 
Analyses of whole plants growing in soil, water culture and other 
media have afforded much information with regard to the relative 
intake of different substances by living normal plants. The long series 
of ash analyses of various plants made by Wolff (1864-1880) and 
others has shown that compounds of potassium, sodium, calcium, 
magnesium and iron, and compounds containing chlorine, sulphur, 
phosphorus and silicon are present in considerable quantity in prac¬ 
tically all plants examined, and it must be therefore concluded that 
such compounds are capable of penetrating into the cells of plants. 
Aluminium and manganese also appear to be regular constituents of 
plant ash, though often in very small amount, so it must be supposed 
that compounds containing these substances are capable of pene¬ 
trating through the cell membranes of plants. The relative quantity 
of these various ash constituents varies however in different species 
(cf. for example, Grandeau and Bouton, 1877), and the differences 
cannot be correlated with differences in composition of the medium 
from which the plant obtains its ash constituents, although plants of 
the same species can take in more of any particular constituent from 
a medium which is rich in the constituent than from a medium poor 
in it (cf. Malaguti and Durocher, 1858, for the case of calcium). 
Apart from the work of Salm-Horstmar (1851, 1856) with soil 
cultures and Sachs (i860, 1861) and Knop (i860) with water cultures, 
directed to determine the elements essential for plant nutrition, the 
work of Maze (1913 a, b, 1914), Monnier (1905), Deleano (1907, 
1908 a , b) and Pouget and Chouchak (1913) deserves mention in this 
place, as these authors have used the method of chemical analysis to 
determine the intake of different mineral constituents at different 
stages in the development of the plant. Their results were obtained, 
however, from the point of view of the part played by inorganic salts 
