PHYTO-PHYSIOLOGY. 261 



1379. The physical operation of water consists indeed, 

 for the greatest part, in its preserving the solid parts in 

 a supple or pliant state. Its principal office is, however, 

 to convey nourishment to the plant. 



1380. The earths act beneficially only upon plants, if 

 they have been all mixed with each other. Mineral salts 

 occurring in moderate quantity in the soil promote 

 growth ; alkalies and acids are injurious thereunto. 

 The same holds good of Inflammables and metallic 

 limes. 



b. BY INTERNAL ACTIVITY. 



1381. That the plant imbibes water, and this indeed 

 in great quantity, by its whole surface is a well-ascer- 

 tained fact ; but it has been by no means equally deter- 

 mined whether it obtains its nourishment simply through 

 the water, or directly also from the air, e. g. the carbon, 

 as well as the nitrogen, from the carbonic acid. The 

 principal imbibition, however, takes place through the 

 root ; but experiments that have been made upon this 

 subject leave it doubtful, whether in this case it is sim- 

 ply mucus, extract from the humus or vegetable mould, 

 or simply carbonic acid that has been absorbed. 



1382. It is moreover a fact that the green parts of 

 plants exposed to direct sun-light consume or take in 

 carbonic acid, and develop or give out oxygen ; on the con- 

 trary, during the night, and even in cloudy or gloomy days, 

 they absorb oxygen and exhale or develop carbonic acid. 

 Now, as there are far more gloomy or at least cloudy 

 than clear days, it thus becomes evident that far more 

 oxygen has been taken up, than separated, from the air. 

 During germination oxygen gas is consumed and, on the 

 other hand, carbonic acid developed. 



1383. The saps ascend upwards, and chiefly indeed, 

 in the liber ; on its passage different substances forming 

 from it, which appear especially in the fruit in greatest 

 proportion and variety. 



