58 Bergtheil and Day. — On the Cause of ‘ Hardness ' in 
is made by Percival (2) to the effect that their testae contain an abnormally 
large amount of ash constituents, and that these resist the penetration 
of water. This explanation has been shown inadequate in the case under 
consideration by Leake (loc. cit.),who compared the amount of ash derived 
from testae of seeds of Indigofer a arrecta with that obtained from the seed 
of Indigofer a sumatrana (with the germination of which there is no difficulty) 
grown in the same locality, and found a considerably larger quantity 
in the latter case. 
We have therefore sought for an explanation in the structure, or the 
nature, of the organic constituents of the seed-coat. 
Preliminary examination of sections of the testa in an unstained 
condition, or treated with a simple undifferentiating stain (e. g. carmine 
or haematoxylin), showed its structure to be identical with that character- 
istic of the seeds of other leguminous plants. Superficially there is a layer 
of thick-walled ‘ palisade ’ cells with their longer axes parallel to the radii 
of the seed ; beneath this is another layer of thick-walled cells of peculiar 
shape whose contents are pigmented yellow, and beneath this layer again, 
a double row of elongated cells with their longer axes parallel to the 
circumference of the seed ; finally, there are several layers of ordinary paren- 
chymatous tissues (PI. VII, Fig. i). No essential difference could be found 
in the structure of the testae of the seeds of Indigofera arrecta and Indigo - 
fera sumatrana , and in neither case could any traces of substances of 
a waxy nature be detected, either by examination of untreated sections 
or sections treated with osmic acid. 
In order to ascertain how far water could penetrate into the hard 
seed-coat, sections were cut of seeds which had remained in' water con- 
taining a little fuchsin for twelve hours without showing any signs of 
swelling. It was found that the stain had not penetrated beyond the 
outermost layer of the seed, and was deposited there in a sharp line (Fig. i). 
On similarly examining seeds of Indigofer a sumatrana , or those of Indigofera 
arrecta which had been scarified or previously treated with sulphuric acid, 
the stain was found to penetrate to the innermost layer of the testa 
(Fig. 2). 
This seemed to clearly indicate that the resistant layer was to be 
found at the extreme outside of the hard seeds, and a careful examination 
was therefore made of the chemical nature of the substances composing 
the ‘ palisade ’ cells. On treating sections of such seeds with chlor-zinc- 
iodine (Schulze’s solution), the cell-walls of all the tissues swelled and 
acquired the violet colour characteristic of cellulose, and the cell-contents 
the yellow colour indicating the presence of proteid substances. No cuticle 
could be detected by this treatment, and sections of the testa of Indigofera 
sumatrana seeds, and those of Indigofera arrecta , after treatment by 
scarifying or acid, presented an identical appearance to those of untreated 
