32 



SEEDS AND SEEDLINGS. 



of water coloured with red ink ; keep the apparatus in a fairly warm 

 place, and note any visible result. 



After a day or two, when you find that no more water seems to 

 be collecting at the bottom of the jar, raise the cork and insert a 

 lighted taper. Now write out an exact account of what has hap- 

 pened during this experiment. What changes in the air have been 

 wrought by the germinating seeds ? Why does the water pass over 

 through the bent tube from the vessel outside into the jar ? 



* (b) In the last experiment the carbon dioxide produced by the 

 germinating seeds was absorbed by the caustic potash solution in the 

 sponge. Omit the latter this time; half-fill the jar (Fig. 19) with 

 soaked Peas or Beans, and fix the bent tube so that the end of one 

 limb is above the level of the seeds, while the outer limb dips into 

 a bottle containing lime-water or baryta-water. Set the apparatus 

 in a warm place, and notice the bubbles of carbon 



dioxide which are given off, and which cause a 

 white precipitate. 



* (c) Take three U -tubes and three narrow jars 

 (or test-tubes a little wider than the U -tubes). 

 Place in one arm of each U-tube (Fig. 20) six 

 soaked seeds (Peas or Wheat), then invert the 

 U-tube after inserting a cork, with a wad of 

 soaked cotton-wool to keep the seeds moist. 

 Half-fill the jars or test-tubes with (1) water, 

 (2) strong caustic potash solution, (3) strong 

 solution of pyrogallol in caustic potash, and place 

 the open ends of the U -tubes in the test-tubes. 

 If you have no suitable narrow jars, support the 

 test-tubes in a stand. 



Notice that in (3) the solution soon rises in 

 the inverted (J-tube (how far does it rise, and 

 why ?) and the seeds germinate very little (why ?) ; 

 in (2) the solution rises, more slowly, and to the 

 same extent (why ?), and the seeds germinate well ; 



in (1) the water hardly rises at all, though germination occurs as in 

 (2). What has happened in each case? In (2) the seeds absorb 

 oxygen from the air and give out carbon dioxide, which is absorbed by 

 the potash solution, and the latter therefore rises slowly in the (J-tube 

 for about a fifth of its length ; in (3) the potash and pyrogallol solution 

 absorb the oxygen of the air in the U -tube. Why does the water not 

 rise in (1)? 



Fig. 20. 



57. Intra-molecular Respiration. In the foregoing 

 experiments it is clear that normal germination does not 

 occur unless the seed is supplied with air containing oxygen. 

 In some cases, however, a slight amount of growth occurs 

 even when the seeds are deprived of oxygen, and sometimes 



