104 Mr. Knight on the Direction of 
general extension of parts already formed : and the new 
matter which is thus successively added unquestionably de- 
scends in a fluid state from the cotyledons.* On this fluid, 
and on the vegetable fibres and vessels whilst soft and 
flexible, and whilst the matter which composes them is 
changing from a fluid to a solid state, gravitation, I conceive, 
would operate sufficiently to give an inclination downwards 
to the point of the radicle ; and as the radicle has been proved 
to be obedient to centrifugal force, it can scarcely be con- 
tended that its direction would remain uninfluenced by gra- 
vitation. 
I have stated that the radicle is increased in length only by 
parts successively added to its point: the germen, on the 
contrary, elongates by a general extension of its parts pre- 
viously organized ; and its vessels and fibres appear to extend 
themselves in proportion 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 
perpendicular direction, the sap must accumulate on its under 
side : and I have found in a great variety of experiments on 
the seeds of the horse chesnut, 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 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 
* See Phil. Trans, of 1805. 
