sap does not even cease during the night, but 

 goes on unintermittently ; and as there is always 

 a considerable quantity of carbonic acid taken up 

 along with the moisture by the roots, but which, in 

 the absence of sun-light, cannot be assimilated, we 

 consequently find it expelled by the stomata of the 

 leaves. Vital power is, however, not altogether 

 extinct during the night, for an absorption of 

 oxygen undeniably takes place, which element is, 

 retained in the system, to take part in some 

 chemical process not quite understood as yet. 



Hydrogen and oxygen, which next claim our 

 attention, we find in most of the vegetable com- 

 pounds in the relative proportion of 1 to 8 the 

 same proportion in which they form water ; so 

 that it has been correctly inferred that water is the 

 source from which the different organs of plants 

 derive and assimilate these two elements. But 

 water has several functions to fulfil in vege- 

 table life ; for it not only furnishes hydrogen 

 and oxygen to assist in the direct formation of the 

 different parts of the plant, but also serves 

 as the sole medium by which all the mineral 

 substances derived from the soil pass into the 

 vegetable system. It serves as a solvent for 

 all the inorganic food which plants require, and 

 which it thus renders assimilable. 



On account of these various functions which 

 water has to fulfil, it is absolutely indispensable for 

 all vegetation, and therefore without it no plant 



