CH. V] SWELLING OF WOOD. 107 



after the first interval of 24 hours has elapsed. Pick out 

 all the seeds which have not swollen, and in half of them 

 pierce the testa with a needle, leaving the other half 

 intact. It will be found that all the punctured seeds 

 swell within 12 hours, whereas only a percentage of the 

 intact seeds are swollen\ 



(138) Rise of temperature accompanying imbibition. 



Prepare enough dry powdered starch^ to make a layer 

 about an inch thick at the bottom of a beaker, and place 

 a similar quantity of water in a second beaker. When 

 starch and water are at the same temperature, pour the 

 water into the first beaker, stir with a thermometer bulb, 

 and note the rise of a few degrees which takes place. 



(139) Work done during imbibition. 



Saw out a square inch from a deal board of about 

 j of an inch in thickness. Put it in a flat photographic 

 dish and let it serve as a support for a 28 lb. weight. On 

 adding water the wood swells and raises the weight, a 

 movement which may be recorded in various ways, e.g. by 

 a horizontal microscope, or by the micrometer-screw 

 described below, experiment 155. The weight will com- 

 press the dry wood slightly, so that it is necessary to 

 wait until the index comes to rest before the water is 

 added. 



1 See Detmer, Praktikvm, p. 131. 



' The starch should be dried at 100° C. and may be allowed to eool, 

 without special precautions, to the room-temperature, when it will still 

 be sufficiently dry for our purpose. 



