The Light Relation 



427 



of light and darkness upon the form and growth of plants 

 has been much investigated. In most cases no adequate 



FIG. 119. Sun print show-ing difference in opacity (thickness and chlo- 

 rophyll content) of celery leaves grown in half-shade (left) and in sun- 

 light (right). 



consideration has been given to other factors than light, 

 but in general the response to light is so much more marked 



