4 GERMINATION OF THE SEED. CHAP. I. 



till the radicle appeared. The tube was then in- 

 verted and the radicle immediately began to bend 

 itself downwards. The tube was again inverted, 

 and the radicle resumed its original direction.* 

 How ac- < Such is the invincible tendency of the radicle 

 for by the to fix itself in the soil, and of the plumelet to es- 



phytolo- ca P e * nto *^e a * r " U w i s this tendency to be 

 gists. accounted for ? A great many conjectures have 

 been offered in reply to the inquiry, but without 

 having done much to elucidate the subject. Some 

 have attributed the phenomenon to the excess of 

 the specific gravity of the juices of the radicle be- 

 yond that of the juices of the plumelet, which in 

 their progress upwards were supposed to be reduced 

 by elaboration to a light vapour. But this is not 

 known to be the fact, or rather it is known not to 

 be the fact, and consequently forms no ground of 

 argument. Others have attributed it to the re- 

 spective action of the sun and earth ; the former 

 attracting the leaves and stem, and the latter at- 

 tracting the root. But it happens rather unfortu- 

 nately for this conjecture, that the phenomenon is 

 exactly the same, even when seeds are made to ger- 

 minate in the dark. Du Hamel made the experi- 

 ment in a dark room ; and obtained the same result 

 as in the light. The influence of the sun was then 

 transferred to that of the air, which was thought to 

 have some peculiar attraction for the plumelet, 

 which the earth had not. But the attraction of the 

 * Phys. des Arb, liv, ii. chap, vl 



