Rudide and Germen of Seeds. 127 



riety of experiments on the seeds of the horse-chestnut, the 

 bean, and other plants, when vegetating at rest, that the 

 vessels and fibres on the under side of the germen invariably 

 elongate much more rapidly than those on its upper side; 

 and thence it follows that the point of the germen must al- 

 ways 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, 

 as 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 

 under side is not confined to the germens, nor even to the 

 annual shoots of trees, but occurs and produces the most 

 extensive effects in the subsequent growth of their trunks 

 and branches. The immediate effect of gravitation is cer- 

 tainly to occasion the further depression of every branch, 

 which extends horizontally from the trunk of the tree ; and, 

 when a young tree inclines to either side, to increase that 

 inclination ; but it at the same time attracts the sap to the 

 under side, and thus occasions an increased 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 opposi- 

 tion 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 pre- 

 ceding deductions ; but those I have stated, I conceive to be 

 sufficiently conclusive. It has, however, been objected by 

 Du Hamel (and the greatest deference is always due to his 

 opinions), that gravitation could have little influence on the 

 direction of the germed were it in the first instance pro- 

 truded, or were it subsequently inverted, and made to point 

 perpendicularly downwards. To enable myself to answer 



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

 trees, the cause of which I ha\ « endeavoured to point out in a former memoir, 

 i'hii. Traus. 1801 



this 



