THE VEGETABLE KINGDOM. 



5i: 



ficled to the earth it imbibes water and swells. Soon after- 

 wards the integument tears irregularly and the young 

 plant appears outside. Sometimes, however, this act is 

 effected symmetrically. The seed presents a kind of lid 

 or little door, which the young plant opens by pushing it 

 so as to direct itself towards the soil, as we see in the 

 Indian reeds. After that the root sinks dowuAvards and 

 the stem shoots up towai'ds the light. 



This double i^henomenon has occupied physiologists a 

 great deal. At first the direction of the roots was attri- 

 buted to the humidity of the ground or to its chemical 

 composition. But Duhamel having noticed that young 





kf 



2(i0. Germination of an Arwido indica. 



roots did not sink into Avet sponges between which seeds 

 had been made to germinate, and Dutrochet having re- 

 mai"ked that seeds suspended in boxes filled with earth left 

 them in order to penetrate more deeply, it became neces- 

 sary to renounce these two hypotheses. 



Knight and Dutrochet, seeing that when seeds are made 

 to grow in the buckets of a wheel set in motion by mechan- 

 ism, the rootlets always tend outwards and the stems in- 

 wards, concluded that the divergence of these organs was 

 owing to the influence of terrestrial graAdtation. 



