134 GROWTH OF PLANTS. 



Upright Growth of Plants. 



It may be considered one of the most universal laws 

 of germination, that every part of a plant, except the 

 root, rises in an upright direction from the ground in 

 the same way as the root goes downwards. I have 

 already mentioned the experiments of Mr. T. A. 

 Knight and Dutroehet, who placed germinating plants 

 on wheels revolving both vertically and horizontally, 

 when the stems uniformly tended to the centre of the 

 wheel and the roots to the circumference, which tends 

 to prove that gravitation is the chief agent in causing 

 plants to rise perpendicularly. The same law will 

 account for the side branches bending down, as in the 

 weeping willow and the lime tree, while the main stem 

 rises upwards. Lord Kames mentions an ash tree 

 growing on the high wall of a ruin, which sent a root 

 down along the wall to the ground; a circumstance 

 easily accounted for on the same principle, though it 

 has been adduced as a proof of instinct, if not of 

 reason itself, in the tree. 



What are termed creeping stems may be thought 

 exceptions ; but the runners ' of the strawberry, and 

 the suckers 2 of the sweet violet, are not by any means 

 stems, but side shoots for the purpose of propagating 

 new plants. 



Weak stems, which are unable to rise high in a 

 perpendicular direction, are furnished with various 



(1) In Latin, Sarmenta. (2) In Latin, Stolones. 



