126 On ihe Direction of the 



dity of the motion of my wheels was sometimes diminished 

 by the collection of fibres of conferva against the wire grate, 

 which obstructed, in some degree, the passage of the water; 

 and the machinery, having been the workmanship of myself 

 and my gardener, cannot be supposed to have moved with, 

 all the regularity it might have done had it been made by a 

 professional mechanic. But I conceive myself to have fully 

 proved that the radicles of germinating seeds are made to de- 

 scend, and their gcrmens to ascend, by some external cause, 

 and not by any power inherent in vegetable life ; and I see 

 little reason to doubt that gravitation is the principal if not 

 the only agent employed, in this case, by nature. I shall 

 therefore endeavour to point out the means by which I con- 

 ceive the same agent may produce effects so diametrically 

 opposite to each other. 



The radicle of a germinating seed (as many naturalists 

 have observed) is increased in length only by new parts suc- 

 cessively added to its apex or point, and not at all by any 

 general extension of parts already formed; and the new 

 matter which is thus successively added, unquestionably de- 

 scends in a fluid state from the cotyledons *. On this fluid, 

 and on the vegetable fibres and vessels whilst soft and flex- 

 ible, and whilst the matter which composes them is changing 

 from a fluid to a solid state, gravitation, J conceive, would 

 operate sufficiently to give an inclination downwards to the 

 point of the radicle ; and as the radicle has been proved to 

 be obedient to centrifugal force, it can scarcely be contended 

 that its direction would remain uninfluenced by gravitation. 



I have stated that the radicle is increased in length only 

 by parts successively added to its point : the gcrmen, on 

 ihe contrary, elongates by a general extension of its parts 

 previously organized ; and its vessels and fibres appear to 

 extend themselves in proportion to the quantity of nutri- 

 ment they receive. If the motion and consequent distribu- 

 tion of the true sap be influenced by gravitation, it follows, 

 that when the germen at its first emission, or subsequently, 

 deviates from a perpendicular direction, the sap must accu- 

 mulate on its under side : and I have found in a great va- 

 • See Phil. Trans, of 1805. 



riety 



