66 PRINCIPLES OF GARDENIXG. [CH. II. 



food by the agency of their roots ; and the extremi- 

 ties of these appear to be the chief, if not the only 

 parts employed, in the intro-susception of all food not 

 in a gaseous state, for M. Duhamel observed that 

 that portion of a soil was soonest exhausted in which 

 the greatest number of the extremities of the roots 

 were assembled. — [Physique des Ai'bres, vol. iii. 

 p. 276.) 



M.M. Sennebier and Carradori brought this to the 

 test of direct experiment, and fomid that if roots of 

 the carrot, scorzonera, and radish are placed in 

 water, some mth only their extremities immersed, 

 and others with their entire surfaces plunged in, 

 except the extremities, the foimer imbibe the 

 water rapidly, and the plants continue vegetating ; 

 but the others imbibe no perceptible quantity, and 

 speedily wither. It suggests also the reason why 

 the gardener, in applying water or manure to trees 

 or shrubs, does so at a distance from their stems. 

 A good rule for ascertaining the proper distance for 

 such applications, seems to be to make them beneath 

 the circumference of the head of the tree ; for, as M. 

 De Candolle observ^ed, there is usually a relation 

 between that and the length of the roots, so that 

 the rain falling upon the foliage is poured off most 

 abundantly at the distance most desirable for reach- 

 ing the extremities of the roots. 



This explains why the fibrous points of roots are 



