204 CONSERVATIVE ORGANS. [LECT. V. 



gate in that city, and which I have seen, explains 

 it in the following manner: " Here the vital 

 powers of the tree not being adequate, from scanty 

 nourishment, to the usual annual degree of 

 increase in the branches, were accumulated in the 

 root, which, therefore, was excited to an ex- 

 traordinary exertion, in its own natural direction 

 downwards." I would, however, say that it was 

 owing to the moisture of the earth soaking into 

 and ascending the wall, a fact which, from every 

 day's experience, we know takes place, that the 

 root extended in the direction of its natural stimu- 

 lus, the moisture ; the real exciting cause of its 

 increased exertion : and the accuracy of this 

 opinion is placed almost beyond controversy, by 

 the experiment of Mr. Knight, which I am about to 

 relate. Some Beans were placed in pots filled with 

 earth, but were half covered only with the mould. 

 The pots were then inverted on a grating of wood, 

 so as to support the earth and the Beans, in such 

 a manner, that the earth was above and the air 

 beneath each radicle as it was emitted. Water 

 was next introduced through the bottom of the 

 inverted pots : the radicles extended horizontally 

 along the surface of the mould, and in contact with 

 it ; and in a few days emitted many fibrous roots 

 upwards into it, which passed through one half of 

 the mould. We may, therefore, venture to assert, 

 Jhat although the natural direction of the radicle 



