1 28 On the Diredtion of the 



this objection I made many experiments on seeds of the 

 horse-chestnut, and of the bean, in the box I have already 

 described ; and as the seeds there were suspended out of the 

 earth. I could regularly watch the progress of every effort 

 made by the radicle and germen to change their positions. 

 The extremity of the radicle of the bean, when made to point 

 perpendicularly upwards, generally formed a considerable 

 curvature within three or four hours when the weather was 

 warm. The germen was more sluggish ; but it rarely or 

 never failed to change its direction in the course of 24 hours ; 

 and all my efforts to make it grow downwards, by slightly 

 changing its direction, were invariably abortive.- 



Another, and apparently a more weighty objection to the 

 preceding hypothesis, (if applied to the subsequent growth 

 and forms of trees,) arises from the facts that few of their 

 branches rise perpendicularly upwards, and that their roots 

 always spread horizontally; but this objection, I think, may 

 be readilv answered. 



The luxuriant shoots of trees, whieh abound in sap, ki 

 whatever direction they are first protruded, almost uniformly 

 turn upwards, and endeavour to acquire a perpendicular di- 

 rection ; and to this their points will immediately return if 

 they are bent downwards during any period of their growth; 

 their curvature upwards being occasioned by an increased 

 extension of the fibres and vessels of their under sides, as in 

 the elongated germens of steds. The more feeble and slender 

 shoots of the same trees will, on the contrary, grow in al- 

 most every direction, probably because, their fibres being 

 more drv, and their vessels less amply supplied with sap, 

 they are less affected by gravitation. Their points, however, 

 generally show an inclination to turn upwards ; but the ope- 

 ration of light, in this case, has been proved by Bonnet* to 

 be very considerable. 



The radicle tapers rapidly as it descends into the earth, 

 and its lower part is much compressed by the greater solidity 

 of the mould into which it penetrates. The true sap also 

 continues to descend from the cotyledons and leaves, and 



• Rt'cherches our I'Usage iei FeuHles-dam !es P'antes. 



occasions 



