144 GERMINATION, GROWTH, TISSUE TENSION. 



paper on the outside of the jar. Fit up a " control " experiment in 

 which a cork with a thermometer hangs into a jar containing some 

 water but no seeds. Note the rise of the cork as the Peas swell 

 and push it up, and compare the temperatures, at the beginning 

 and end of the experiment, in the jar containing the Peas and that 

 containing water (or that of the surrounding air). 



(d) Does imbibition cause rise of temperature in dead substances 

 as well as in seeds ? Put some powdered starch into a tumbler, to 

 form a layer about an inch deep, put an equal amount of water into 

 another tumbler, and set a thermometer into each. When the two 

 temperatures are equal, pour the water over the starch, stir with 

 the thermometer, and note the rise in temperature (how many 

 degrees ?). 



(e) If a small wooden box (e.g. a cigar-box with the lid fastened 

 down by tacks) is filled with dried Peas and then immersed in 

 water, it will burst as the Peas absorb water and swell. Try this 

 experiment. A large mass of swelling Peas may lift a weight of 

 more than 100 Ib. 



(/) The force exerted by swelling seeds can also be shown by 

 filling an ordinary narrow-necked bottle with Peas, and placing it 

 under water in a basin ; the bottle should be left uncorked, and 

 some rubber bands should be put round it to prevent the shattered 

 glass from being thrown out. Another method is to fill with dry 

 Peas an empty rabbit-skull and let it lie in water ; the bones will be 

 torn apart along the seams (sutures) where they join each other. 



(g) How is the absorption of water by seeds affected by tempera- 

 ture ? Weigh about 30 grams of dry Beans or Peas, place them 

 in a beaker of water at 35 C. , set the beaker on a sand-bath with a 

 thermometer in the water, and keep the temperature steady at 

 35 C. for two hours. At the same time place an equal weight of 

 seeds in cool water, with a thermometer ; first let the water stand 

 for a time till it acquires the temperature of the room. At the end 

 of two hours, wipe dry both lots of seeds and compare the increase 

 in weight in each case. The seeds that have been kept in water at 

 35 C. will have absorbed from two to three times as much as those 

 kept in the cool water. 



(h) Weigh about 30 grams of dry Peas and place them in a 

 10 per cent, solution of salt in a beaker or tumbler. At the same 

 time put a similar weight of Peas in distilled water (or tap water). 

 Compare the weights of the two lots of seeds after two hours, 

 wiping them dry before weighing. Which lot has increased most in 

 weight ? 



185. Effects of Heat on Seeds. When a seed is exposed to a 

 fairly high temperature for a few hours all the water it contains 

 is driven off, and the young plant is killed, we can only tell whether 

 a seed is alive or not by ascertaining whether it will germinate when 



