272 APPLICATION OF PRINCIPLES. 



fully attended to and often shifted, are so much mora 

 healthy than those treated otherwise. It is not, how- 

 ever, merely for the purpose of removing deterio- 

 rated earth or adding manure, that shifting is impor- 

 tant ; all potted plants have, in time, their ball of 

 earth, by the continual passage of water through it, 

 reduced to a state of hardness and solidity unfavour- 

 able to the retention of moisture or the growth of 

 roots ; and this is of course cured, if the operation of 

 shifting is judiciously performed. I must, however, 

 confess, I have seen gardeners contented with lifting 

 a plant, with a hard old matted ball, out of one pot 

 into another of a little larger size, shaking some par- 

 ticles of fresh earth in between the ball and the side 

 of the pot, and pressing the whole down with as much 

 force as the thumbs can give. 



It is found that the' roots of potted plants invariably 

 direct themselves towards the sides of the pot, as must 

 indeed necessarily happen in consequence of their dis- 

 position to grow horizontally. Having reached the 

 sides, they do not turn back, but follow the earthen- 

 ware surface, till at last they form an entangled stra- 

 tum enclosing a ball of earth ; then, if not relieved 

 by repotting, they rise upwards towards the surface, 

 or they attempt to force themselves back to the centre. 

 The greater part, however, are always found in con- 

 tact with the porous earthen side of the vessel ; and 

 especially all the most powerfully absorbent, that is, 

 youngest parts. They are, therefore, in contact with 

 a body subject to great variations of temperature and 

 moisture, in consequence of exposure to the sun, or to 



