VEGETABLE ABSORPTION. 17 



the case with by far the greater nninber, the roots 

 are the special organs to which this office of ab- 

 sorbing nourishment is assigned : but it occasion- 

 ally happens that, under certain circumstances, the 

 leaves or the stems of plants are found to absorb 

 moisture ; which they have been supposed to do by 

 the stomata interspersed on their surface. This, 

 however, is not the natural action of stomata ; and 

 they assume it only in forced situations, when the 

 plant can procure no water by means of the roots, 

 either from its having been deprived of these organs, 

 or from its being left totally dry. Thus a branch, 

 separated from the trunk, may be preserved from 

 witliering for a long time, if its leaves be immersed 

 in water ; and when the soil has been parched by 

 a long drought, the drooping plants will be very 

 quickly revived by a shower of rain, or by artificial 

 watering, even before any moisture can be supposed 

 to have penetrated to the roots. 



It is by the extremities of the roots alone, or 

 rather by the spongioles which are there situated, 

 that any regular absorption takes place ; for the 

 surface of the root, being covered in every other 

 part by a layer of epidermis, is incapable of per- 

 forming this office. It was long ago remarked by 

 Duhamel, that trees exhaust the soil only in those 

 parts which surround the extremities of the roots ; 

 but the fact that absorption is effected only at those 

 points has been placed beyond a doubt by the direct 

 experiments of Sennebier, who, taking two carrots 

 of equal size, immersed in water the whole root of 

 the one, while only the extremity of the other was 

 made to dip into the water, and found that equal 

 quantities were absorbed in both cases; while on 



VOL. H. c 



