226 



The Living Plant 



And for answer we turn to experiment. If seeds of mustard or 

 radish are started in water-culture vessels, by methods described 

 in an earlier chapter (page 136), the young seedlings grow rigidly 

 upright in darkness; but if, when well started, they are given a 



FIG. 75. Sets of Radishes grown side by side in a chamber lighted wholly from the right 

 hand side; but those on the instrument were kept continually revolving. 



one-sided light, they turn always as shown in our figure, the 

 stems to the light and the leaves across it as before, but the roots 

 distinctly away (figure 76). And such conduct is typical of or- 

 dinary stems, leaves and roots. 



This process of light-turning is called in physiology Photo- 



