THJS WOBK OF STEMS 269 



Grape Vine, Corn, Sunflower, Corn-stalk or any pithy- 

 stem) a piece at least a foot long, carefully remove a 

 thin slice from the outer part of the stem and place it 

 in water ; trim away everything from the pith, take a 

 slice from it and place it in water beside the other. 

 Both slices must be the full length of the piece of 

 stem. Keep both slices under water, and examine at 

 the end of twenty -four hours. Which has grown the 

 more ? A further illustration of this inequality of 

 growth may be had by splitting a Dandelion stalk 

 (see Fig. 152) lengthwise into four pieces and placing 

 in water (other pithy or succulent stems or stalks 

 may be treated in the same way) . 



The rigidity of the tip of the stem is also largely 

 due to the fact that the cells are filled with water 

 under pressure (just as in the case of the root -hair, 

 see page 123), which renders them rigid. Cut off the 

 tip of an herbaceous stem two or three inches in 

 length, place it in a strong solution of salt or sugar 

 for an hour or so. Explain the result. Place a wilted 

 stem in the apparatus shown in Fig. 140 or 141, 

 and force water into it under pressure. 



As a result of all these devices, the herbaceous 

 stem is a model of strength, lightness and elasticity, 

 serving its purpose perfectly; and we may say that 

 this problem has been exceedingly well solved. In 

 the case of tree trunks, the mere accumulation of 

 woody material provides the necessary strength ; while 



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