56 
Walter Stiles 
tion of sulphuric acid, while in the presence of acid the pigment 
changes in colour to red. 
In a subsequent paper A. J. Brown (1909) showed that less water 
is absorbed by barley grains from salt solutions than from pure 
water, a result to be expected if the covering of the grain contains 
a semi-permeable layer (compare Chapters VI and VIII). 
Such semi-permeable membranes formed by cell walls have been 
shown by A. J. Brown (1907) to be present also in grains of Avena, 
Secale and Triticum, the semi-permeable membrane of the last 
named having also been investigated by Schroeder (1911). Gassner 
(1915) also records the presence of semi-permeable cell layers in 
seeds of Gramineae, while they have been observed by Tjebbes (1912) 
in sugar-beet seed, by Shull (1913) in the seeds already mentioned 
and in apple, pear, Vicia Faba and other Leguminosae, Helianthus 
annuus, Xanthium gldbratum and Alisma plantago-aquatica, and by 
Rippel (1918) particularly in JEsculus hippocastanum and to a less 
extent in a number of other species. Rippel soaked seeds in a solution 
of IV/10 sodium chloride, measured the uptake of water by weighing 
the seeds, and the intake of sodium chloride by titrating the solution 
against silver nitrate. He showed that generally speaking the greater 
the intake of water, the greater the intake of salt. His results are 
summarised in Table XVII. 
Table XVII 
Relation of Semi-permeability of Seeds of Various Species 
to Water Intake (from Rippel) 
Species 
Trifolium pratense 
Sinapus alba 
Phaseolus multiflorus 
Pisum sativum I 
II 
Vicia Faba 
Lychnis Githago 
Rye 
Cannabis sativa 
^Fsculus hippocastanum 
Water uptake 
% 
141-2 
118-0 
106-4 
87-4 
84-0 
65-2 
6o-o 
48-5 
48-2 
21-8 
Ratio of concentration of 
external solution to the 
theoretical concentration 
at the end of the experi¬ 
ment if the seeds are 
completely semi- 
permeable 
56-6 
64-3 
90-0 
82-5 
85*9 
9i‘3 
98-4 
94'3 
95*8 
ioo-o 
Rippel suggests that these results may be explained on the view 
that the swelling of the seed by absorption of water ruptures the 
semi-permeable membrane. 
