100 PHYSIOLOGICAL VIEWS. 



some cotton into a tumbler of water, and put upon it some seeds of rye or wheat, 

 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 ^ig. 121. 



about the sixth day ; at c is the primordial leaf,* which at first 

 envelops and conceals the otlier leaves ; at d are the several 

 branches of the root, bearing their radicles, and at their base envel- 

 oped by a peculiar covering, c,\ through which the extremities have 

 forced their way. 



a. Earth, though not absolutely essential to germination, is useful, 

 as aftording to the vegetable it^g a favoiable situation, where it 

 may receive the influence of the various agents which are to per- 

 form their offices in tlie development of its parts. But plants may 

 vegetate without earth. The parasite grows upon the bark of 

 other plants, or feeds on air alune ; and many seeds vegetate in 

 water, .^i/- 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 sufiiciently 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 canics it off in the form of carbonic acid. Air furnishes 

 that important agent, oxygen, which is the first moving principle of vitality. Car- 

 bon constitutes the greater part of the substance of seeds ; and this principle, being 

 in its 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 absence 

 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 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 cannot 

 be made to vegetate. The process of moJting 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 difference in plants as to their term of germinating ; some 

 •eeds begin to vegetate before they are separated from the pericarp.:J: In the 



* Called by Mirbel the pUeole. 



t The coleorhize. 



X In the month of January, on observing the see<1s of a juicy apple which had been kept in a warm 

 jellar, I saw that they were swollen, and the outward coat had buri^t ; examining one seed, by re- 

 moving ihe integument and separating the cotyledons, I saw, by the help of a microscope, the embryo 



Explanation of Fig. 121 — n. Earth important to vegetation — Air— Oxygen — Carbon — The absence 

 of light favorable to the germination of plants — Heat — b. Season of germinating. 



