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 



m \ 







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- 

 dinarv stems, leaves and roots. 



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



