On the Food of Plants. 
505 
is, merely subject to the laws which govern ordinary molecular 
actions. 
Starch is found abundantly in nearly all the tissues of plants ; 
stem, leaves, roots, seeds are occasionally charged with it almost, 
in appearance, to bursting ; it is only necessary to instance the 
common potato, grain of all kinds, the roots of the orchis and 
arum, as examples. When these are torn to pieces by grating 
and placed in a little trickling stream of water, the starch is 
washed out of the cellular tissue which contained it, and on the 
water being allowed to stand, settles down as a white silky powder, 
which under a lens exhibits the appearance of rounded, trans- 
parent, colourless granules, the magnitude of which varies very 
much with the plant from which they were obtained. 
Different microscopic observers by no means agree concerning 
the intimate structure of these granules : some put them down 
for little membranous bladders filled with transparent viscid 
liquid, while others think they have seen enough to convince them 
that the little bodies in question are composed of concentric layers 
of solid gummy matter, covered on the outside by a kind of skin 
impermeable to water : all seem to agree, however, about the 
membranous covering. 
When starch is put into cold water, and the temperature 
gradually raised to the boiling point, this membrane gives way 
as if by the expansion of the matter within, solution takes place, 
and a translucent jelly, familiar in the case of common arrow-root, 
is produced. This change once effected, it is easy to understand 
that a return of the starch to its former organized condition is 
impossible. 
If to gelatinous starch we add a little dilute sulphuric acid, and 
boil the whole for a few minutes, the mixture becomes limpid as 
water, and in that state is found to contain a peculiar gummy 
matter called "dextrine," an isomeric* modification of gelatinous 
starch. If, however, the ebullition be continued for a longer 
period, the new substance undergoes further change, and passes 
into sugar of the variety contained in fruits. During this action 
the sulphuric acid undergoes no change, nothing is taken up from 
the air, and no gaseous matter given off. 
When grain is made to germinate, barley for example in malt- 
ing, a part of the insoluble starch passes into sugar, and at tlie 
same time a peculiar principle called "diastase" is generated 
from the azotized matter of the grain. This diastase has the re- 
markable property of occasioning, when present in very small 
quantity, the conversion of starch into grape sugar at all tempera- 
tures, from that of ice to near the boiling point of water. Hence, 
* Same composition reckoned to 100 parts. 
