9-6 



GERMINATION OF THE SEED. CHAP. I. 



By Mr. Knight has also more recently attempted to 



account for the descent of the radicle upon the old 

 but revived principle of gravitation ; strengthened, 

 as he no doubt thinks, by the result of the follow- 

 ing experiments. Beans which were made to ger- 

 minate, after being fastened in all positions to the 

 circumference of an upright and revolving wheel, 

 that performed 150 revolutions in a minute, uni- 

 formly directed the radicle outwards from the 

 centre, and the plumelet inwards to the centre. 

 Beans that were so fastened to a horizontal and 

 revolving wheel, protruded their radicles obliquely 

 outwards and downwards ; and their plumelets 

 obliquely inwards and upwards. These effects Mr. 

 Knight regards as resulting from the centrifugal 

 influence of the wheel's motion counteracting that 

 of gravitation, which is consequently in his opinion, 

 in the natural situation of the seed, the cause of 

 the radicle's descent.* But if gravitation acts so 

 very powerfully upon the radicle, why will it not 

 condescend to exert its influence upon the plumelet 

 also, which, if not so heavy as the radicle, is at 

 least specifically heaver than atmospheric air ? And 

 why does it make an exception in favour even of 

 some radicles. The radicle of the seeds of the 

 Missletoe, though adhering merely to the under 

 surface of a bough and originally protruding itself, 

 as it must sometimes unquestionably do, in the 

 direction of the earth's surface, will yet in oppo- 

 * Nichol, Journ. vol. xiv. p. 4-10. 



