GERMINATION, GROWTH, TISSUE TENSION. 149 



(a) Plant some Beans about 3 in. deep in moist soil or sawdust 

 in a flower-pot, and pack stiff clayey soil (or plasticine) firmly above 

 them. Watch them to see whether they emerge at the sides or 

 whether they push the whole mass of clay upwards. 



(b) Invert a short test-tube over a Bean seedling with a plumule 

 about 3 in. long, then place over this a vertical glass tube open at 

 both ends, inside which the test-tube can slide freely, and clamp 

 this tube to a support. Into the upper end of the open tube place 

 a second test-tube containing mercury or shot. Mark with a paper 

 strip the level of the top of the shoot, and see what weight of 

 mercury or shot is required to prevent the shoot from continuing 

 to grow upwards. Another method is to use a spring inside a 

 closed tube in place of the mercury or shot ; measure how much 

 the force of the shoot, pushing up its tube, compresses the spring, 

 then find what weight is needed to compress it to the same extent. 



(c) You have probably used mercury in various experiments, and 

 know that it is a very heavy liquid (13| times heavier than water). 

 Fix a seedling (Bean, Pea, etc., should be tried) to the side of a 

 small dish containing mercury with a layer of water above it, and 

 see whether the root will grow down into the mercury. The seeds 

 may be pinned to a cork which is securely fixed to the rim of the 

 dish (e.g. a saucer) by making a slit in it and jamming it tightly on 

 the rim ; each seed should of course be fixed by two pins. 



(d) Fix a young Bean seedling so that its root grows in a small 

 tube filled with moist soil or sawdust, and place this tube within 

 a larger one containing a spring. The root grows downwards with 

 a force equal to over 300 grams (about 11 oz.) ; measure the 

 diameter of the root and calculate the force it exerts per square 

 centimetre or square inch. 



191. Effect of Removal of Cotyledons. Deprive 

 Beans, Peas, and other germinating seeds of both of their 

 cotyledons in some cases just after the seed has been 

 soaked, in others after the radicle has grown 5 cm. long, 

 in others after the plumule has grown 5 cm. long. In 

 each case place some of these seeds, along with untouched 

 seeds for comparison, in the light ; and place others, also 

 with untouched control seeds, in darkness. 



192. Effect of Removal of Foliage-leaves. Kemove 



the foliage-leaves from (J.) a young Bean plant which has 

 not yet used up the food in its cotyledons, (B) an older 

 seedling whose cotyledons have fallen off (if they have 



