100 
PHYSIOLOGICAL VIEWS. 
Bome cotton into a tuntbler of water, and put upon it some seeds of rye or wheats 
all the fibres shooting from the seeds will seek a direction downward. 
Fig. 121 represents a young plant of rye, which is monocotyle- 
donous ; at a is the cotyledon ; at b, the second leaf, which appears Fig- 121. 
about the sixth day ; at c is the primordial leaf,* which at first 
envelops and conceals the other leaves ; at d are the several 
branches of the root, bearing their radicles, and at their base envel- 
oped by a peculiar covering, €,\ through which the extremities have 
forced their way. 
a. Earth, though not absolutely essential to germination, is useful, 
fts aftordhig to tlie vegetable egg a favoiable situation, where it 
may receive the influence of the various agents which are to per- 
form their offices in the development of its parts. But plants may 
vegetate without earth. The parasite grows upon the bark of 
other plants, or feeds on air alone ; and many seeds vegetate in 
water. Air is essential to vegetation ; — under an exhausted receiver 
a seed will not germinate, although possessing every other requisite. 
Seeds that become imbedded deeply in the ground do not vegetate 
unless accidentally plowed up or otherwise exposed to the contact 
of the atmosphere. Acorns supposed to have been long buried have 
germinated as soon as raised sufficiently near the surface of the earth to receive 
the influence of air. 
We have seen, in the process of germination, that oxygen gas unites with the 
carbon of the seed, and carries it off" in the form of carbonic acid. Air furnishes 
that important agent, oxygen, which is the fir.'^^^t moving principle of vitality. Car- 
bon constitutes the greater part of the substance of seeds ; and this principle, being 
in itp nature opposed to putrefaction, prevents seeds from rotting previous to their 
being sown. Some seeds, having an abundance of carbon, are capable of being 
preserved for many years ; while others, in which this element exists but in a small 
proportion, require to be sown almost as soon as ripe ; and such as are still more 
deficient in carbon lose their vital principle before separating from the pericarp. 
Oxygen is therefore important to germination on account of its agency in removing 
the carbon which holds the living principle of the seed in bondage. The absentee 
of light is favorable to the germination of seeds, for light acts upon plants in such 
a manner as to take away oxygen by the decomposition of carbonic acid gas, and 
to deposit carbon ; now this is just the reverse of the process required in germi- 
nation, where the carbon must be evolved and the oxygen in excess. A certain 
degree of heat is necessary to germination. Seeds planted in winter will remain in 
a torpid state ; but as soon as the warmth of spring is felt the embryo emerges 
into life. By increasing heat the vegetating process may be hastened ; thus the 
same seed, which with a moderate degree of heat would germinate in nine hoursj 
may be brought to this state in six hours by an increase of temperature. Too 
great heat d-estroys the vital principle ; thus corn which has been roasted cannot 
be made to vegetate. The process of malting consists in submitting some kind of 
grain (barley is most commonly used) to a process which causes an incipient state 
of germination ; this is done by moistening the grain, and exposing it to a suitable 
degree of warmth ; as soon as germination commences the process is stopped by 
increasing the heat. The taste of the grain is then found to have become sweetish. 
The term malt is given to grain which has been submitted to this process. When 
mixed with water it forms a sweetish liquor, and the fermentation of this liquor 
produces beer. 
b. There is a great diff^erence in plants as to their term of germinating ; some 
eeeds begin to vegetate before they are separated from the pericarp.;}: In the 
* Called by Mirbel the pileole. 
+ The coleorkize, 
% In the month of January, on observing the seeds of a juicy apple which had been kept in a T»arm 
eellar, I saw that they were swollen, and the outward coat had burst ; examining one seed, by re- 
noving ihe integument and separating the cotyledons, I saw, by tlie help of a microscope, the embryo 
Explanation of Fig. 121— n. Earth important to vegetation — Air— Oxygen — Carbon — The absenc« 
of light favorable to the germination of plants — Heat — b. Season of germinating. 
