124 



VII. ON THE DIRECTION OF THE RADICLE AND GERMEN DURING THE 

 VEGETATION OF SEEDS. 



[Read before the ROYAL SOCIETY, January 9, 1006.] 



IT can scarcely have escaped the notice of the most inattentive observer 

 of vegetation, that in whatever position a seed is placed to germinate, its 

 radicle invariably makes an effort to descend towards the centre of the 

 earth, whilst the elongated germen takes a precisely opposite direction ; 

 and it has been proved by Duhamel * that if a seed, during its germina- 

 tion, be frequently inverted, the points both of the radicle and germen 

 will return to the first direction. Some naturalists have supposed these 

 opposite effects to be produced by gravitation ; and it is not difficult to 

 conceive that the same agent, by operating on bodies so differently orga- 

 nised as the radicle and germen of plants are, may occasion the one to 

 descend and the other to ascend. 



The hypothesis of these naturalists does not, however, appear to have 

 been much strengthened by any facts they were able to adduce in support 

 of it, nor much weakened by the arguments of their opponents ; and 

 therefore, as the phenomena observable during the conversion of a seed 

 into a plant are amongst the most interesting that occur in vegetation, 

 I commenced the experiments, an account of which I have now the 

 honour to request you to lay before the Royal Society. 



I conceived that if gravitation were the cause of the descent of the 

 radicle, and of the ascent of the germen, it must act either by its imme- 

 diate influence on the vegetable fibres and vessels during their formation, 

 or on the motion and consequent distribution of the true sap afforded by 

 the cotyledons : and as gravitation could produce these effects only 

 whilst the seed remained at rest, and in the same position relative to the 

 attraction of the earth, I imagined that its operation would become 

 suspended by constant and rapid change of the position of the germi- 

 nating seed, and that it might be counteracted by the agency of centri- 

 fugal force. 



Having a strong rill of water passing through my garden, I con- 

 structed a small wheel similar to those used for grinding corn, adapting 

 another wheel of a different construction, and formed of very slender 

 pieces of wood, to the same axis. Round the circumference of the 

 latter, which was eleven inches in diameter, numerous seeds of the 

 garden bean, which had been soaked in water to produce their greatest 

 degree of expansion, were bound, at short distances from each other. 



* Physique des Arbres. 



