118 SWELLING OF SEEDS. [CH. V 



renewed to minimise decomposition, and this should be 

 done at intervals of 12 hours until all the seeds are 

 swollen, noting at each examination the number of freshly 

 imbibed seeds. 



The cause of the individuality in imbibition seems to 

 depend, not on the cotyledons, but on the seed-coats. 

 This may be demonstrated on a similar number of seeds, 

 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 1 . 



(138) Rise of temperature accompanying imbibition 9 . 



Prepare enough dry powdered starch 3 to make a layer 

 2 3 cm. 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 

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

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

 adding water the wood swells and raises the weight, a 



1 See Detmer, Praktikum, p. 131. 



2 Nageli, Theorie d. Gahrung, 1879, p. 133. 



3 The starch should be dried at 100 C. and may be allowed to cool, 

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

 be sufficiently dry for our purpose. 



