THE CONTROL OF LIFE 101 



but it largely determines the position 

 assumed by the leaf and in many cases 

 modifies its external form. Thus the 

 harebell (Campanula) produces leaves 

 of a very diflFerent shape on a branch 

 which is covered so as to exclude light. 

 The water hyacinth (Eichornia) loses in 

 the shade to a considerable extent the 

 remarkable swollen leaf stalk filled with 

 air which assists the plant to float on the 

 surface of the water. 



Light modifies the color and the fra- 

 grance of flowers, as well as of other parts 

 of the plant. Reducing the amount of 

 light by shading plants for a part of each 

 day causes some species to produce 

 flowers and fruit very much earlier, 

 while in other cases the reverse occurs, 

 as shown by the experiments of Garner 

 and Allard. 



Marked modifications arc produced in 

 some cases by temperature. Every one 

 has noticed the manner in which plants 

 at high altitudes hug the ground, in many 

 cases forming rosettes which spread out 



