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YEGETABLE PHYSIOLOGY. 
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of the development at an earlier stage than in the more perfect embryos, since the germs that do exist 
are cellular masses just like those of the more perfect forms before their cotyledons are formed. 
During the ripening of seeds the cells of the albumen, or of the cotyledons, become filled 'with 
collections of accumulated nutriment in the form of starch, oil, or mucilaginous matters, or in some 
cases in the form of secondary layers thickening the walls of the cells ; at the same time the greater 
part of the water is removed and the seed becomes dried to a certain extent, the chemical activity of 
its contents is arrested, and it remains in a state of rest until excited to new development by exposure 
to heat and moisture. Different seeds have very different degrees of power of persistence in this state 
of rest, but it is striking to note what great resistance many offer to external influences. The seeds of 
the Cereals have been found to bear a short exposure to a heat of 112° Fahr. in water, 140° in steam, 
and 168° in dry air, as well as a dry cold of 90° below the freezing point. Under favourable conditions 
some will retain their germinative power for centuries ; others decay if not sown almost immediately 
they are ripe ; this is the case especially with seeds containing much mucilaginous matter, which is 
readily decomposed. 
As the seed unfolds, the assimilated matter in the cells of the cotyledons, or the albumen, becomes 
dissolved and converted into gummy or saccharine matters, which are at once applied to the nourishment 
of the young plant. In some cases even a portion of the cellular structure is dissolved and assimi- 
lated ; this is the case with some kinds of cereals ; more frequently there exists a much greater store 
within the cells than is necessary for the plant before its rootlet becomes capable of absorbing fresh 
matters ; and as is especially noticed in seeds with abundance of horny albumen, a large portion of this 
matter is left untouched. The decomposition of the store of nutriment is accompanied by the absorption 
of oxygen, the separation of carbonic acid, and the temperature of the seed rises. It is not clear at 
present whether this expenditure of the carbon of the seed, by being burnt, as it may be termed, with 
the elevation of the temperature, is a part of the assimilative process, or is a separate process having 
merely for its object the liberation of heat to act as a stimulus upon the nascent organs ; but the necessary 
consequence is, as experiment has also shown, a loss of weight of organic matter during the germination. 
There are few points concerning which more has been said and written than on the cause of the 
direction taken by the opposite extremities of the axis of the nascent plant, of the downward growth of 
the root and the upward of the terminal bud. One of the most universally adopted views has been 
that which explains the growth downward of the radicle by gravitation. Mr. Knight stated that he 
made roots grow in an oblique direction by causing the seeds to germinate on a revolving wheel so 
that the centrifugal force partly counteracted the gravitation. Whether this experiment would show 
a constant result is uncertain, but even if it did it would not suffice to prove that gravitation, was the 
cause of the root penetrating the earth, for the portion which grows upward is frequently the heaviest 
end, and yet at the same time, rises in a lighter medium. Moreover, the mode of germination of the 
Misletoe and other parasites upon the stems of trees shows that the direction is governed by some much 
more special influence than the universal law of gravity. So far as we are in a position to tell, there 
is some definite, and as yet unknown, cause which makes the radicle first grow towards the earth or other 
source of nourishment, which it penetrates by elongation, a resisting point being ottered by the weight of 
the seed or the earth covering it ; and then, in its further growth downward, it requires a point of 
resistance to be afforded by the adhesion of the earth around the collar of the root, since the elongation 
takes place in the structures just above the point of the root, thus exerting a pressure upwards and 
downwards, which if the upper part of the root be kept tree, and the weight of the plant balanced, will 
cause the whole to rise bodily upwards. Thus when seeds germinate in damp moss lying upon a hard 
Surface, the elongation of the root will push the stem up through the moss, unless the root branches so 
as to get fixed down by entanglement among the loose matters. 
We may admit, therefore, that we are at present totally ignorant of the cause of the direction taken 
by roots, all the notions hitherto advanced having been purely speculative. 
The time which is required for germination depends greatly upon the texture of the coats of the 
seed, and in particular on the covering it may possess belonging to the fruit: naked seeds Usually 
germinate much sooner than those enclosed in a seed-vessel, like the acbenes of the Rose tribe \c. It 
is worthy of remark that many of the seeds which are enclosed by a hard shell or stone, germinate 
naturally in the midst of a decaying pulp, which must contribute to the decomposition of the shell. 
Soaking such seeds in water or causing them to pass through the digestive canal of animals, as by 
feeding fowls on the Hawthorn fruits, greatly accelerates germination. 
Almost all the questions relating to the chemical changes which on air during germination remain 
to be cleared up, which can only he done by the co-operation of chemists with practised veg< table 
anatomists, a conjunction greatly to he desired for vegetable physiology generally. It is in the power 
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