106 THE ROOT. 



and solid, is of course specifically heavier than the 

 water, and on this account it sinks ; but in the succeed- 

 ing year it also will produce a new plant aad knob, and 

 being itself exhausted it will swim, and fade and decay 

 in its turn."* 



With respect to direction, roots exhibit some vari- 

 ations worthy of our attention. The spindle shaped 

 are generally perpendicular, gradually tapering as they 

 proceed downwards, but the fibrous and branching roots 

 are more frequently horizontal, sometimes near the 

 surface, and sometimes deep in the earth, accommo- 

 dating themselves to the climate and soil in which they 

 grow. An experiment has often been made of planting 

 seed in sand over a bed of rich earth, and it is found 

 that the root descends several inches below its usual 

 situation, apparently in search of the more congenial 

 soil beneath it. Wildenow placed a Strawberry plant 

 in some sand close to the rich soil of a garden, and it 

 exhibited some evidence of the same selective proper- 

 ty, by growing towards the good soil in which it conti-' 

 nued to flourish long after the main plant had decayed. 

 A more singular case has recently occurred in Scotland. 

 A seed of the Plane tree was accidentally deposited on 

 the ruinous wall of a monastery in Galloway, where it 

 germinated, and the young tree grew for a while with 

 considerable luxuriance, though the wall on which it 

 stood was ten feet from the ground. Its small store of 

 nourishment was soon exhausted, and the young tree 

 ceased to grow, but as if it had perceived the rich sup- 

 ply of food at the bottom of the wall, it sent down some 

 strong fibres which soon reached the earth. When 

 these roots had become attached to the surrounding soil 

 so as to supply the young tree with nourishment, it 

 * Keith 



