182 REVIEW. 



this purpose, they must be carefully excluded from the action of heat and 

 moisture, and other chemical agents. Seeds retain their vitality for a very 

 long period — for hundreds, or even thousands of years. Seeds which have 

 been proved to have been not less than one thousand eight hundred years old, 

 have germinated and produced thriving plants ! and plants have appeared, 

 on turning up the ground in some situations — the seeds of which are con- 

 jectured to ha^e been buried a much longer period. 



" Four conditions are necessary for the process of germination, the pre- 

 sence of water, of heat, and of air, and the exclusion of light. 



" Water softens the integuments, and renders them capable of being burst 

 by the swollen embryo ; dissolves the nutritive matter contained in the seed 

 thus reducing it to a fit state to be absorbed for the nutrition of the em- 

 bryo ; conveys in solution nutritive particles from other sources; and fur- 

 nishes two important ingredients in the composition of vegetables. 



" The air, by means of the oxygen which it contains, effects a chemical 

 change on the farina of the seed. The oxygen combines with the carbon, 

 and forms carbonic acid, which escapes ; and thus the proportion of oxygen 

 and hydrogen being increased by the expulsion of the carbon, the farina is 

 converted into a semi-fluid substance, of a saccharine or mucilaginous na- 

 ture, consisting of starch, gum, and sugar, well adapted for the nutrition 

 of the plant in its infant state. 



" Heat always promotes chemical combination and decomposition, and 

 thus assists the action of the water in dissolving the hard parts of the seed, 

 and that of the air in its part of the process. Most probably heat acts as a 

 general stimulus to the absorbents in the seed. Seeds cannot be made to 

 germinate in very cold weather, except by the application of artificial heat. 

 Too great heat also checks germination, because it destroys the vitality of the 

 seed. 



" Light is unfavourable to germination, because it disposes to an accu- 

 mulation of carbon in ihe seed, and a consequent hardening of the parts, 

 or rather prevents the expulsion of carbon, and consequent softening of the 

 parts, which if necessary they should be taken up and applied to the use of 

 the plant. The seeds of red poppy and charlock remain in the ground and 

 retain their vitality for a long period ; hence they are frequent on new banks 

 or newly upturned ground. 



" From the operation of these causes, it will be seen why seeds planted 

 too deeply in the earth do not germinate. The air has not access to them, 

 and therefore, from the want of that important stimulus, they remain torpid. 

 Hence it is that earth newly dug up frequently becomes covered with weeds, 

 the seeds of which soon germinate when exposed to the air. 



" Placing seeds at a certain depth in the earth excludes them from the ac- 

 cess of light which is so injurious to germination; insures a supply of mois- 

 ture, which would not remain with them were they placed at the surface ; 

 protects them from the wind, and from the attacks of animals, and enables 

 the roots to take a firm footing in the soil. 



" When the germination has commenced, the seeds become soft, and 

 swells, oxyg'en is absorbed, and carbonic acid disengaged ; the particles of 

 the covering of the seed loose their cohesion, and it bursis to make way for 

 the elongation of the embryo ; the radicle elongates and descends, often 

 attaining a considerable length before the gemmule has made any progress, 

 and soon exercises its function of absorbiug food ; the cotyledons expand 

 and become seminal leaves, which afford nourishment to the young plant 

 in the first stage of its existence, by elaborating the sap, and wither when 

 the proper leaves of the piant have unfolded, or remain under the surface, 

 are gradually absorbed, and disappear; the gemmule or first bud gradually 

 unfolds and enlarges ; the leaves and stem appear, and we now have a 

 young plant, a living being, able to provide its own sustenance, and to ap- 

 ply it to its increase, and to the formation of seeds to perpetuate the spe- 

 cies. 



" In the operation of malting, the object is to convert_ the farina of the 



