24 



Introduction to Botany. 



pointing upward, but as the root grows forth it turns sharply 

 downward, and the shoot as it develops, sharply upward. 



This is brought about by the in- 

 fluence of gravity. 



In just what way gravity can 

 exert such an influence is not 

 known. We are accustomed to 

 think of gravity as invariably at- 

 tracting bodies toward the cen- 

 ter of the earth, but on living 

 and growing bodies it may exert 

 an influence of quite another 

 character. We might conclude, 

 without an experiment, that 

 gravity is the directive force ; 

 for whether seeds are germinat- 

 ing near the poles or at the 



equator, the- roots always turn 

 Fig. 6. , , r , , 



„ . , , „ ^ , , toward the center of the earth. 



Fruit of the Cocoanut : A, end view 



of the " cocoanut " or stone of the and the shoots away from it. It 

 fruit (corresponding to the stone j however, a simple matter to 



or a peach), showing the dividing ' ' ^ 



lines of the three carpels which eliminate the directive influence 

 rnX^rt^rLS'^heTotropr of gravity, and by observing the 

 ing. B, longitudinal section growth of secdlings under such 



throuffh the fruit of the cocoanut, . , . ^ a. - ^ i. 



showing the embryo in process of circumstanccs to dctermme what 

 germination ; e, the stone sur- effect gravity is producing Under 



rounding the fleshy endosperm; , ,.^. -r^. 



/ the enlarging cotyledon. The normal Conditions. Figures 7 

 plumule is growing upward and 8, illustrating the result of 



through the fibrous outer coat . 



of the fruit. This coat is re- Experiment 41, page 15, show 

 moved before the cocoanuis are }^q^ the influence of gravity may 



marketed. After Warming. i i • 



be demonstrated by removing it 

 from one set of seedlings while it is still operative on 

 another set. 



