GERMINATION. 787 



Conditions requisite for Germination. — A certain amount of 

 heat and moisture, and a free communication with atmospheric 

 air, are in all cases necessary to the process of germination. 

 Electricity is also considered by some observers to promote it, 

 but its influence in the process is by no means proved, and if 

 exerted it is apparently of but little importance. Light has no 

 influence on germination in most cases, according to Hofl&nann's 

 experiments. 



Moisture is required to soften the parts of the seed and to 

 take up all soluble matters ; the cells of which seeds are com- 

 posed are iu this way enabled to expand, and the embryo to 

 burst through the integuments, but excess of water is often 

 injurious. 



Heat is necessary to excite the dormant vitality of the embryo, 

 but the amount required varies very much in different seeds, 

 and probably each species has its own proper range in this 

 respect. As a general rule from 50° to 80° of Fahr. may be 

 regaKled as most favourable to germination in temperate climates, 

 but some seeds will germinate at a temperature of 35° Fahr. ; 

 and those of many tropical plants require a temperature cf 

 from 90° to 120° Fahr., or sometimes much higher, for germi- 

 nation. 



Air, or at least oxygen gas, is required to combine with the 

 superfluous carbon of the seed, which is thus evolved as carbonic 

 acid, with a sensible increase of temperature, as is well seen in 

 the malting of Barley. The necessity of a proper supply of 

 oxygen is proved by the fact, that seeds will not germinate 

 when buried too deeply in the soil, or when the soil is impervious 

 to air. This explains how seeds may lie dormant at great depths 

 in the soil, and only germinate when that soil is brought to the 

 surface ; and hence we see the necessity of admitting air to seeds, 

 as in the ordinary operations of agriculture. 



Process of Germination.— '^^len the above requisites are sup- 

 plied in proper proportions to suit the requirements of different 

 seeds, germination takes place ; but should either be wanting or 

 in too great amount, the process is more or less impeded, or 

 altogether arrested. The most favourable seasons for germina- 

 tion are spring and summer; and seeds sprout most readily in 

 loose pulverised and properly drained soil, at a moderate depth, 

 for, under such circumstances, air, moisture, and warmth have free 

 access. Seeds thus placed absorb moisture, soften and swell, 

 and certain chemical changes go on at the same time in the sub- 

 stance of the albumen, or, when that is absent, in the cells of 

 the cotyledonary portion, by which a proper supply of nourish- 

 ment is provided for the embryo. These chemical changes chiefly 

 consist in the conversion of starch and other analogous sub- 

 stances which are insoluble and therefore not in a suitable state 

 for absorption, into soluble matters such as dextrin and grape 

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