CHAPTER II 



THE FORM AND ADJUSTMENTS OF THE PLANT BODY 

 TO THE ENVIRONMENT 



We learned in the previous chapter that the organs of the 

 plant body roots, stem, leaves, and flowers were so arranged 

 and adjusted to the materials and forces of the environment 

 as to secure abundant food and energy for the maintenance of 

 life. This necessary arrangement and adjustment of plant organs 

 to their surroundings is secured in part by an inherited plan of 

 architecture, which governs the formation and growth of organs 

 in the embryo and in the adult organisms, and in part also 

 by powers of movement, called tropisms, by which growing 

 plant organs place themselves in proper relations to soil, light, 

 and air. 



THE FORM AND PLAN OF THE PLANT BODY 



If we observe the plant body of most plants, we shall see 

 that it consists of a main stem and root, which constitutes 

 its central axis, and of lateral organs in the form of leaves, 

 flowers, branches, and lateral roots. More careful observa- 

 tion of such a plant will also show that the lateral organs 

 are not placed on the main axis in an indefinite manner, but 

 that they have a definite order and arrangement inherited from 

 a long line of plant ancestors. It will soon become evident 

 also that by this inherited plan of the plant body the organs 

 are so related to each other and to air, light, and soil as to 

 make the plant as a whole a good working organism in its 

 efforts to secure food for sustenance and growth. These facts 

 will become more and more obvious as we proceed to study 

 the relations of leaves, branches, and secondary roots to each 

 other and to the main axis. 



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