Ch. XVI] GERMINATION. 10! 
that in the process of germimation, orygen gas unites with the 
sarbcn of the seed, and carries it off in the form of carbonic 
acid. Air furnishes that important agent, oxygen, which is the 
first moving principle of life. 
420. Carbon constitutes the greater part of the supstunce o: 
seed; and this principle being in its nature opposed to purtre- 
faction, prevent seeds from rotting, previous to their being sown. 
Some seeds having abundance of carbon, are capable of being 
preserved for ages: while others, in which this element exists 
but in small proportions, require to be sown almost as soon as 
ripe; and such as are still more deficient in carbon, lose their 
vital principle before separating frm the pericarp. ; 
421. Oxygen is important tc germination, on account of its 
agency im removing the carbon which holds the living principle 
of the seed in bondage. 
422. The absence of light is unfavourable to the germina: 
tion 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 deposite carbon ; now this is just the reverse of the pro- 
cess required in germination, where the carbon must be thrown 
off and the oxygen in excess. ‘ 
423. 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 
ilfe. By increasing heat, seeds may be hastened in their vege- 
tating process ; thus the same seed, which with a moderate de- 
gree of heat would germinate in nine hours, may be brought to 
this state in six hours, by an increase of temperature. Too great 
heat destroys the vital principle; thus corn which has been 
roasted can never be made to vegetate. 
424, There is a great difference in plants as to their time of 
germinating ; some seeds begin to vegetate before they are se- 
parated from the pericarp.* In the greater number of vegeta- 
* In the month of January, on observing the seeds of a very fine juicy 
apple, which had been kept in a warm cellar, I saw that they were 
swollen, and the outward coat had burst; examining one seed by re- 
moving the tegument and separating the cotyledons, I saw by the help 
of a microscope the embryo, as if in a germinating state; the radicle 
was like a little beak; in the upper part or plume was plainly to be seen 
the tuft of leaves and the stem. 
420. What constitutes the greater part of the substance of the seed 2 
421. Why is oxygen necessary to germination? 
422. Is light favourable to vegetation 
423. Is heat necessary to vegetation ? 
424. What is said of the difference in plants with respect to the time 
of germinati )n ? 
Q* 
