59 
the Seeds of Indigofer a ar recta. 
hard seeds. No explanation of the resistance to water in the latter case 
seemed, therefore, to be provided by this method. Sections treated with 
sulphuric acid and iodine lead to precisely similar results (Fig. 3). 
Several attempts were made to demonstrate the existence of a cuticle, 
in sections of hard seeds by methods of double staining (e. g. aniline-safranin 
counterstained with haematoxylin, and Gram-eosin), but in no case could 
a layer reacting towards these substances in the manner typical of cuticle 
be shown. 
An explanation was eventually found by treating sections with a 
delicate stain for differentiating cellulose and cuticle described by Mangin 
(Zimmermann, 3 ), consisting of a solution of iodine in phosphoric acid. On 
treating sections of the testa of Indigofera ar recta seeds with this reagent, 
the cell-walls of all the tissues and the cell-contents reacted as cellulose and 
proteid matter respectively as before, but after a few minutes’ action, a thin 
yellow line was seen to appear at the extreme periphery of the section, and 
to gradually swell as time progressed. On first appearing, this cuticular layer 
was only about 3-4 /z in thickness, but in the course of a quarter of an hour 
it had become more than three times this depth and was very clearly 
discernible (Fig. 4). Eventually the epidermal cells swelled enormously 
and ruptured, whilst the cuticle split away and was seen as a broad yellow 
band (Fig. 5). On treating sections of seeds of Indigofera sumatrana 
or of ‘ treated ’ Indigofera arrecta with this reagent no layer of this kind 
could be discerned. It was subsequently found that, the cuticular layer 
characteristic of the seeds of Indigofera arrecta could be shown in sections 
treated with a concentrated alchoholic solution of chlorophyll, as recom- 
mended by Correns ( 4 ), but the test is difficult of application and uncertain 
in result. 
It is clear, therefore, that the hard nature of the seeds of Indigofera 
arrecta is due to their possession of a very thin outer covering of a substance 
resistant to water. The exact nature of this substance cannot be de- 
termined by the methods which have been described. By its reaction 
under treatment with chlor-zinc-iodine, its swelling under the action of 
dehydrating agents, and its failure to respond to double staining methods, 
it would appear to consist of cellulose ; whilst by its colour reaction towards 
Mangin’s phosphoric acid and iodine, its staining with an alcoholic solution 
of chlorophyll, and its impermeability to water, it would seem to be cuticle. 
We can only conclude that it consists of a body of an intermediary nature, 
possibly a transition-product, between cellulose and cuticle. 
The action of scarifying the seed is, no doubt, to remove a portion 
of this resistant covering, and so allow of the penetration of water, whilst 
sulphuric acid acts either in a similar manner by leading to the swelling 
of this layer and its eventual rupture, or by converting it into a body akin 
to cellulose and permeable to water. 
