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tissue is the thickest, and therefore tlie 

 most powerful in its action, consequently 

 swelling would bend a slip of such bark 

 inwards or towards its shoot, and such a 

 shoot would be held up by the inward 

 pressure of its bark all round it, as a wall 

 may be propped from both sides. But in 

 the bark of plants, or parts of plants, which 

 grow from the light, such as ivy, the tendrils 

 of climbing plants, &c., the outside layer 

 of tissue is the strongest ; and the tops 

 of the shoots of such plants tend to stand 

 upright by the pulling outward of their 

 bark from all sides, like the mast of a 

 ship. But light, by increasing the giving 

 off of water (transpiration), decreases swell- 

 ing, and when it falls unequally on plants, 

 the forces on the illumined side will be 

 weakened, and the shoot, according to the 

 formation of its cellular tissue, will be 

 turned either towards or from the light. 

 Thus ivy, or the tendrils of climbing 

 plants, are turned from the light towards 



