VEGETATION OF SEEDS» 413 



I have stated that the radicle is increased in length only by And also in the 

 parts successively added to its point. The gernien, on the con- S^"" 

 trary, elongates by a general extension of its parts previously 

 organized ; and its vessels and fibres appear to extend them- 

 selves in prpportion to the quantity of nutriment they receive. 

 If the motion and consequent distribution of the true sap be 

 influenced by gravitation, it follows, that when the germen at 

 its first emission, or subsequently, deviates from a perpendicu- 

 lar direction, the sap must accumulate on its upper side ; and 

 thence it follows, that the point of the germen must always turn 

 upwards. And it has been proved, that a similar increase of 

 growth takes place on the external side of the germen when the 

 sap is impelled there by centrifugal force, f:s it is attracted by 

 gravitation to its under side when the seed germinates at rest. 



This increased elongation of the fibres and vessels of the ''^''^s ^^i^'^ 

 .... /- 1 1 T effect of gravi- 



under side is not connned to the germens, nor even to the an- tation takes 



nual shoots of trees, but occurs and produces the most exten- Pl^ce in the 



branches of 

 sive effects in the subsequent growth of their trunks and trees. 



branches. The immediate effect of gravitation is certainly to 

 occasion the further depression of every branch, which ex- 

 tends horizontally from the trunk of the tree ; and when 

 a youn^ tree inclines to either side, and thus occasions an in- 

 creased longitudinal extension of the substance of the new 

 wood on that side,* the depression of the lateral branch is 

 thus prevented ; and it is even enabled to raise itself above its 

 natural level when the branches above it are removed ; and 

 the young tree, by the same means, becomes more upright, in 

 direct opposition to the immediate action of gravitation, 

 nature, as usual, executing the most important operations by 

 the most simple means. 



I could adduce many more facts in support of the preceed- Inversion of 

 ing deductions ; but those I have stated, I conceive to be suf- profusion of 

 ficiently conclusive. It has, however, been objected by Du ^^^ germen 

 Hamel (and the greatest deference is always due to his opini- vent the effect, 

 ons), that gravitation could have httle influence on the direc- 

 tion of the germen, were it in the first instance protruded, or 



* Tills effect does not appear to be produced in what are called 

 weeping trees ; the cause of which I have endeavoured to point 

 out in a former memoir. Philo:. Trans. 1804. 



