INTRODUCTORY n 



hand its environment suits its constitution, it has to 

 adapt its structure to the duty of absorbing from the 

 soil what the latter will afford. So the two duties of 

 anchorage and absorption exist together, and the 

 differentiated root system necessarily discharges both. 



If we turn to inquire what dangers beset the part of 

 the plant we have called the shoot, which grows up 

 into the air and forms a head that is frequently of 

 large size, we find them taking shape in the various 

 atmospheric changes incident to every climate. First 

 of these we may place wind or tempest. As the shoot 

 body grows it must offer more and more resistance to 

 air currents, a resistance which may easily culminate in 

 a violent uprooting of the plant. This involves such a 

 subdivision of the plant body as will allow the wind to 

 penetrate through it without serious disturbance. Here 

 we see one meaning of the tapering boughs and twigs, 

 which become more and more flexible as they become 

 increasingly slender. In the central part of the shoot 

 system they are rigid and can resist the storm; where 

 by their dimensions resistance becomes impracticable we 

 find flexibility, enabling them to bow to the wind often 

 so completely as to place their long axes parallel to the 

 direction in which it is blowing. 



Yet another reason for this continued subdivision of 

 the plant body is found in its relation to the absorp- 

 tion from the soil which we have found associated with 

 the root. The latter is continually absorbing the water 

 of the soil ; after separating from such water the mineral 

 constituents it contains, a very large part indeed of the 

 water is evaporated, and so passes away to the exterior 

 again. To favour such evaporation it is advantageous 

 that the ratio between surface and bulk shall be a large 

 one, and so the great subdivision of the subaerial part 

 of the plant is concerned in solving the problem of its 

 nourishment. 



