MOVEMENTS OF GROWTH. 



395 



germination conditions. It is further instructive to experiment 

 with seedlings (say Pisum) whose roots have already attained a 

 length of a few cm., placing them in vessels of water free from 

 air, and isolated from the atmosphere by mercury, and then re- 

 placing the water in one vessel with air, that in the other with 

 Hydrogen. In the air the roots of the seedlings continue to grow, 

 but they do not grow at all in the Hydrogen, as can readily be 

 proved by measuring. 



In the manner described, it can also be shown that the germina- 

 tion of the seeds will take place in a gas mixture very poor in 

 Oxygen (a mixture, e.g., of air with larger or smaller quantities of 

 Hydrogen). 



In order to demonstrate very exactly that the higher plants 

 cannot grow in absence of Oxygen, we proceed as follows. In a 

 test-tube (Z?, Fig. 131), about 15 mm. in diameter and about 60 c.c. 

 in capacity, we fix a 

 pea seedling, raised in 

 sawdust, on whose 

 root ink-lines have 

 been painted as marks. 

 The inside of the test- 

 tube is moistened with 

 a few drops of boiled- 

 out water. The test- 

 tube is closed with a 

 well-fitting two-holed 

 rubber stopper. 

 Through one hole 

 passes the glass tube 

 <7, through the other 

 the tube g\ of which 

 one limb can be dipped 

 into mercury contained 

 in the vessel Gf. In 

 order to drive out the 

 air completely, we now 

 pass a stream of Hy- 

 drogen through the FIG. 131. Apparatus for proving that roots are unable 

 apparatus for one to to grow in absence of free Oxygen ' 

 two hours, and then fuse up the tube g at the point s. The 

 Hydrogen may be prepared, say in a Kipp's apparatus (see 102), 



