THE WORK 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- p^ 



sary 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 



