THEORY OF VEGETATION. 43 



produce oxygen gas in water. 3d. That light is es- 

 sential to vegetable transpiration ; as this process 

 never takes place during the night, but is copious 

 through the day ; and, 4th. That plants raised in the 

 dark abound in watery and saccharine juices, but 

 are deficient in woody fibre, oil, and resins ; whence 

 it is concluded that saccharine compounds are 

 formed in the night, and oil, resins, &c., in the day. 



When the weather is at or below the freezing 

 point, the sap of plants remain suspended and hard- 

 ened in the alburnum ;* but, on the application of 

 heat, whether naturally or artificially excited, this 

 sap is rendered fluid, is put into motion, and the buds 

 begin to swell. Under the same impulse, through 

 the medium of the earth, the roots open their pores, 

 receive nutritive juices, and carry them to the heart 

 of the plant. The leaves being now developed, 

 begin and continue the exercise of their functions, 

 till winter again, in the economy of nature, sus- 

 pends the operation of the machine. Nor is the ac- 

 tion of heat confined to the circulation of vegeta- 

 ble juices; without vapour (its legitimate offspring), 

 the fountain and the shower would be unknown ; 

 nor would the great processes of animal and vege- 

 table fermentation and decomposition go on. With- 

 out rain or other means of ameliorating the soil, 

 what would be the aspect of the globe * what the 

 state of vegetation 1 what the situation of man ? 



The universal diffusion of electrical matter, found 

 in the air and in all other substances, furnishes a 

 presumption that it is an efficient agent in vegeta- 

 tion. Nollet and others have thought that, artifi- 

 cially employed, it favoured the germination of 

 seeds and the growth of plants ; and Davy " found 

 that corn sprouted more rapidly in water positively 

 electrified by the voltaic battery than in water neg- 

 atively electrified."! These opinions have not es- 



* Knight's Observations, &c. f Davy's Elements. 



