503 
On the Food of Plants. 
there is no difficulty in understanding the production of sugar in 
germination. 
Tlie function known to be performed by starch in the vegetable 
kingdom is one of extreme importance. 
The great event in the life of every jdant is the fertilization and 
subsequent development and ripening of its seeds,, and to this end 
the whole energies of the plant are directed from the very com- 
mencement of its being. Up to the time of flowering, provision 
is being made against the cvtraordinary demand for nourishment 
by the young ovules, and this provision is effected by the produc- 
tion of insoluble starch out of the then abundant sweet and gummy 
juices of the plant, •which is stored away in the cells of its tissue, 
until such time as its presence is required to feed the ovule, when 
it is again converted into soluble matter, and conveyed to the spot 
where it is wanted. Arrived there, a large proportion of it is 
reconverted into starch, and laid up within the integuments of the 
seed, once more to pass into the soluble condition, when the time 
for the development of the embryo shall come. 
The starch of a plant has been compared to the fat of an 
animal : a sort of reserved fund of nutritious matter laid up in 
times of plenty to guard against the destruction which must ensue 
when the demand for assimilated food, for vegetable blood, greatly 
exceeds the capacity of the organization to furnish. We must be 
careful not to push the parallel to any extent, since, according to 
views now held by those most competent to judge, the great use 
of animal fat is to supply fuel to a kind of combustion at the 
expense of the oxygen of the air, which goes on, not in the lungs, 
but in the minute circulating vessel.-?, and the end of which is the 
production of animal heat. 
It is obvious that in the phenomena discussed, one-half only of 
the process is intelligible to us, namely, the passage from the inso- 
luble to the soluble state ; we cannot doubt that this is due to the 
agency of diastase, or some such substance ; but how to account 
for the opposite change ? We must still have recourse for the 
present at least to some occult vital principle. 
It is probable that the formation of woody fibre occurs much in 
the same manner out of the semi-fluid substance (cambium) 
found beneath the bark of a tree in active vegetation. We can, 
by a particular process, convert this lignin into gum and sugar : 
the reverse change is beyond our power ; but the operations of 
nature, even on the supposition that the change is purely chemical, 
are not limited to our imperfect methods of proceeding. 
Vcf/etable Acids. — These are found in the juices of all plants, 
usually in a state of combination with potash, soda, ammonia, or 
some of the earths, which remain behind (except ammonia) after 
the destruction of the plant by fire in the state of carbonates. 
