[412 



VEGETATION OF SEEDS. 



to. deviate SO degrees noni the perpendicular direction each 

 would have take-n, ha(i it vegetated at rest. Gradually dimin- 

 ishing the rapidity of the motion of the horizontal wheel, the 

 radicie descended more perpendicularly, and the germens grew 

 inc".<'> uprigiit ; and when it did not perform more than 80 re- 

 volutions in a minute, the radicle pointed about 45 degrees 

 below, and the gerinen as much above, the horizontal line, the 

 one always receding from, and the other approaching to, the 

 axis of the wheel. 

 Kemarks on I would not, however, be understood to assert that the ve- 



aJcm?cvof the ^°^'^y °^ ^^^ ^^ ^^ ^^ horizontal revolutions in a minute will 

 e::periments. always give accurately the degrees of depression and elevation 

 of the radicle and germen which I have mentioned ; for the 

 rapidity 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 mi^^ht have done, had it been made by a profes- 

 sional mechanic. But I conceive myself to have fully proved 

 that the radicles of germinating seeds are made to descend, and 

 their germens 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 v/hich I conceive the same agent may 

 produce effects so diametrically opposite to each other. 

 Observations The radicle of a germinating seed (as many naturalists have 



b" *^j^°?^^'^^ observed) is increased in length only by new parts successively 

 vity produces added to its apex or point, and not at all by any general ex- 

 positiouhfthe ^^'^^'^^ of parts already formed : and the new matter which is 

 radicle. thus successively added, unquestionably descends in a fluid 



state from the cotyledons.* On this fluid, and on the vegetable 

 fibres and vessels whilst soft and flexible, and whilst the matter 

 which composes them is changing from a fluid to a solid state, 

 gravitation, I 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 vi'ould remain 

 uninfluenced by gravitation. 



* See Philos. Trans. 1805. 



I have 



