GERMINATION, GROWTH, TISSUE TENSION. 143 



Notice the drops of water which condense in the colder 

 upper part of the tube. 



(6) Weigh about 30 Peas or Beans, and then dry them 

 thoroughly without scorching or charring them at all. 

 This is best done by placing the seeds for a few hours in an 

 oven, or by means of a sand-bath or a water-bath. Then 

 compare the weight of the thoroughly dried seeds, and 

 the percentage weight of water which the " dry " seeds 

 originally contained (usually about 10 per cent.). This 

 amount of water, though not sufficient to allow of germina- 

 tion taking place, is evidently necessary for the seed to 

 remain alive and capable of germinating. 



A simple water-bath consists of two tin cups and an 

 iron tripod to rest them on ; half fill one cup with water, 

 and into it put the other cup containing the seeds to be 

 dried. A simple sand-bath consists of a shallow tin or 

 pan filled with sand, supported on a tripod and heated 

 below as usual, the seeds being placed in a smaller tin or a 

 saucer resting on the sand. 



184. Absorption of Water by Seeds. (a) Keep some "dry" 

 seeds in a drying-oven or drying-bath until they show no further 

 loss in weight, and then find out whether they swell up in water 

 and whether they germinate. The results will show that killed 

 seeds still have the property of absorbing water. 



(6) When a dry seed is placed in water, how much does it absorb, 

 and what proportion do the volume and weight of the absorbed 

 water bear to the volume of the dry seed? Weigh twenty dry 

 Beans ; pour water into a graduated vessel until it reaches the 150 c. c. 

 , then drop in the beans, and shake the vessel to 



mark, then drop in the beans, and shake the vessel to get rid of any 

 air present ; the rise in level gives the volume of the Beans. Take 

 them out and place them in moist sawdust for two days, then wipe 

 them dry, weigh them, and find their volume as before. If you 

 have no graduated vessels, use a glass jar with a strip of paper, 

 marked into inches or centimetres, gummed on the outside of the jar. 

 Beans absorb about 130 per cent, of their own weight of water. 



(c) The swelling of seeds by imbibition of water can be easily 

 demonstrated to a class. Put about 30 grams of dry Peas and 

 an equal amount of water into a narrow cylindrical glass jar. 

 Cover the Peas with a cork ; smear the edges of the cork so that it 

 can slide inside the jar, and pass a thermometer through a hole 

 bored in its centre. Weigh the cork down with lumps of lead or a 

 number of weights and mark its position by gumming a strip of 



