68 EXPERIMENTS WITH PLANTS 



x 



stem, kill it with boiling water, place in water and 

 observe whether there is any growth, i. e., increase 

 of weight or length, and whether such growth "sets." 



Inasmuch as wood and many other substances 

 derived from plants (and animals) possess the prop- 

 erty of swelling up in water, even when dead, it may 

 be interesting to compare them with seeds in this 

 respect. Test the swelling power of dead, dry wood 

 in the same apparatus which you have used for seeds. 



How much water does the wood absorb ? Wood 

 has the power of taking moisture from the air to such 

 an extent that it has been used to foretell changes 

 in the weather by means of thin strips, which warp 

 in opposite directions as the air grows moister or 

 drier. 



A very important practical question is, whether 

 wood swells equally in all directions. Draw two lines 

 ten inches long on a piece of dry plank, one with 

 the grain, the other at right angles to it. Keep the 

 piece of wood under water for two or three weeks, 

 and then remeasure. Find out something about the 

 behavior of different kinds of wood in shrinking, 

 warping, etc., and the practical bearings of these facts. 



These experiments will serve to give clear ideas 

 about certain physical aspects of growth which are of 

 very general application. 



