TEE WOBK OF STEMS 



265 



potted plants (especially seedlings of Grasses, Radish, 

 etc.) in a box which admits light through an opening 

 on one side only (or shade the plants as they grow, 

 so as to accomplish the same result) . The effect of 

 different kinds of light may be shown by covering the 

 opening with a flat flask or bottle filled in one case 

 with a solution of potassium bichromate, in the other 

 with ammoniacal copper sulphate (i. e., blue vitriol 

 dissolved in water with the addition of ammonia to 

 give a beautiful blue color) . The first transmits red, 

 orange, yellow and a part of the green rays; the 

 second the rest of the green, together with blue, 

 indigo and violet rays. 



As the plant grows taller and develops a larger 

 crown of foliage, the stem is exposed to greater and 

 greater strains from the action of the wind. How to 

 secure the neces- 

 s a r y strength 

 with the smallest 

 outlay of mate- 

 rial is a problem 

 which we may 

 now consider. If 

 we fasten a small 

 beam securely at 

 one end and attach a weight to the other, as shown in 

 Fig. 146, the beam will tend to bend and take the posi- 

 tion shown by the dotted lines; the upper surface 



w 



::A. 



ft- 



146. Diagram showing 

 effect of weight ap- 

 plied to the end of a 



