62 BIOLOGY OF PLANTS. 



perature requisite to the germination of the various seeds, 

 which are cultivated upon the farm ; hence, too, we see the 

 reason and necessity of green and hot houses, to produce the 

 requisite temperature for the germination of those seeds, which 

 are to furnish the earlier vegetables. Heat further promotes 

 germination, by producing those transform-ations which must 

 take place in the starch and gum of the seed, and which 

 both the external heat,, and that generated within the seed 

 duing the process, is employed in producing. 



4. Light was formerly supposed to retard the process of ger- 

 mination, but according to the experiments of M. de Saus- 

 sure, it takes place in the same space of time, in the light as 

 in darkness, provided the light does not, by the heat contained 

 in it, dry up the skins of the seed ; but as this generally takes 

 place, the burying of the seed in the soil a few inches is 

 most favorable to the process, as the light is excluded, while 

 heat, moisture and air are freely admitted. 



The process of germination then, and the changes which 

 take place, may be reduced to the following particulars. 



L Water penetrates the coats of the seed, causing it to 

 swell, which facilitates the introduction of the oxygen con- 

 tained in the water, and in the atmosphere to all its parts. 



2. The oxygen of the water thus introduced combines chem- 

 ically with the carbon which is the principal substance of the 

 seed, forming carbonic acid ; and the oxygen of the air with 

 the hydrogen of the water, forming water. The carbonic acid 

 acts upon the alkalies,* and these react upon the vegetable 

 matter and convert it into vegetable food. 



3. The caloric necessary to the process increases the chem- 



* When woody fibre or vegetable matter is brought into contact with 

 any alkali, it enters into a process of rapid decay, and is soon convert- 

 ed into a substance capable of being held in solution by the water, and 

 of entering the organs of plants. Jlence the use of potash, lime, etc. 

 in the process of germination, and during the growth of plants. Alka- 

 lies are powerful converters of vegetable matter into food. 



