14 BOTANY 



the ground. In this way they present their edges to 

 the wind, and offer as little obstacle as possible to its 

 passage through the tree, so making as small as possible 

 the risk of being torn off when the force of the wind is 

 strong. As the wind passes between them they are 

 made to rise and fall, but they offer much less resistance 

 to its force than they would if they were not flattened. 



The arrangements of the plant and its parts so far as 

 we have studied them are such as to secure its firm 

 attachment to the soil, its stability in storms, with rela- 

 tion both to wind and rain. They also make possible 

 the absorption of liquid, containing mineral matters, 

 from the soil ; the evaporation of the excess of water so 

 absorbed ; the free interchange of gases between it and 

 the air; the needed facilities for the manufacture of 

 sugar from the gases absorbed from the air and the 

 water from the soil. They are, in fact, suitable to 

 support and nourish a stationary living organism and 

 to furnish defences against the most evident dangers to 

 which it is exposed. 



The establishment of such a position by the plant 

 is carried out by means of growth alone. It is a gradual 

 process, therefore, and must be accompanied by the 

 nutritive processes which enable growth to take place 

 First among these comes the supply of the material for 

 the increase of size which we associate with growth. 

 We have seen that the plant absorbs from the soil cer- 

 tain mineral compounds dissolved in water, and from 

 the air certain of its constituent gases. The most 

 important of the materials which the earth yields are 

 nitrates of potassium, calcium, and other metals, phos- 

 phates of the same, traces of compounds of iron, a little 

 silica in some combination, together with the water in 

 which they are dissolved ; carbon dioxide is supplied by 

 the air. When the absorption of these substances is 

 possible, and when light is sufficient and temperature 



