On the Cause of ‘Hardness' in the Seeds of 
Indigofera arrecta. 
BY 
C. BERGTHEIL and D. L. DAY. 
With Plate VII. 
I T is well known that seeds possessed of hard coats, which do not allow of 
the penetration of water and consequent germination, frequently occur 
in certain leguminous plants, but no satisfactory explanation of the cause 
of this phenomenon has, so far as we are aware, been yet given. Attention 
has been drawn to the very marked case of hardness in the seeds of 
Indigofera arrecta by Leake ( 1 ), who points out that in the seed of this 
plant derived from Natal or grown in India the germination capacity 
normally varies from 5 to 10 per cent., but that by suitably scratching 
the seed-coat, in the manner commonly practised in the case of clover^ 
it may be made to very nearly approach 100 per cent. These observations 
have been confirmed, and have been found to apply equally to seed derived 
from Java. The matter has assumed considerable industrial importance 
owing to the introduction of hidigofera arrecta , as a substitute for the 
previously grown Indigofera sumatrana , into the indigo districts of Bihar, 
and machines have been devised for scarifying the seed in bulk, in such 
a manner as to render its germination capacity satisfactory. 
It has recently been found that the same end could be gained more 
simply, and with more certainty of success, by treating the seed with 
concentrated sulphuric acid ; the seed resists the attack of this substance 
for twenty minutes to half an hour, and, after washing and drying, is found 
to germinate perfectly 1 . 
As a result of this observation it seemed to us of interest to try to 
determine to what cause the hardness of the seed was due, and how this 
cause was removed by scarification, and by treatment with acid. The only 
suggestion we have been able to trace as to the cause of hardness in seeds 
1 The idea of using sulphuric acid arose out of certain experiments carried out by Dr. Butler on 
the destruction of the eggs of insect pests in the lint of cotton-seed by treatment with this substance, 
after which, the germination capacity of the seed was found to be considerably improved. 
[Annals of Botany, Vol. XXI. No. LXXXI. January, 1907.] 
