t48 PROCESS OF NUTRITION. CHAP. Ilk 



receiver without lime was only five grains in the 

 same space of time, though it appeared by the 

 application of lime water that the proportion of 

 carbonic acid remaining after the experiment was 

 T y T . Saussure explains the phenomenon thus : 

 the great quantity of carbonic gas evolved by plants 

 in the shade is prejudicial to their vegetation at 

 least in confined atmospheres ; but a partial priva- 

 tion of the gas thus produced is beneficial to their 

 vegetation.* 



The foregoing experiments were made upon 

 plants vegetating in pure water j but Saussure made 

 some experiments also on plants vegetating in the 

 earth, by means of enclosing part of a bough in a 

 large globe of glass. The results obtained were 

 upon the whole similar to the former; but in the 

 case of the decay of the leaves by their exposure 

 to the sun and to the action of lime, the effect was 

 produced more slowly. It should be recollected, 

 however, that the cases are not precisely similar ; 

 for though the plants were in both cases equally 

 deprived of the external action of carbonic acid ga* 

 upon their leaves ; yet there was a supply of that 

 gas communicated to the plant from the oil in the 

 one case that could not have been communicated to 

 it in the other. 

 By the as- The elaboration of carbonic acid then in plants 



aimilation . . . 



of its car- exposed to the sun is unquestionable: but in what 

 evolution state is '* actually assimilated to the plant ? Is it 

 Xy " 'Snr.laVeg.chap.* 



