132 



MISCELLANEOUS. 



PT. II, 



gradations, till tlieir roots shall stand on the base of the 

 hanger. The long one-sided columns of green will be 

 submerged, smothered, and killed below the one com- 

 mon level of the tops, and the plants will be deprived 

 almost entirely of their organs of respiration and trans- 

 piration. But besides this greater space for the heads, 

 there is also greater space for the roots of plants 

 growing on the side of a hill, than if they had only the 

 base of the hill-side to grow on. For roots, as has 

 been shown (page 86), have the power of following 

 the surface of the earth, be the inclination upward or 

 downward what it will. And they do not grow solely 

 vertically downward like the tap-root of a seedling. 

 In reference to an entire hill, of a given base, this 

 increase of surface or space for the roots will be not 

 only directly as the height of the hill, but also directly 

 as the steepness of its sides. Taking one side of a hill, 

 if the side forms an angle of 45° with the horizon, its 

 additional surface or space for roots, as compared 

 with its base, will be as the diagonal is to the side of a 

 square. 



In the south of Europe and Madeira the steep hill- 

 sides are terraced with stone walls, in order to arrest 

 the soil, which would otherwise be washed down by 

 rain. Here there would be a loss of superficies for 

 the roots, and the hill-side would afford them no more 

 space than the area of its base. But the vine stocks 

 are huilt in horizontally through these stone walls, and 

 their roots planted in the earth behind them which is 



