CHAP. III. 
ORIGIN OF WOOD. 
263 
No doubt aware of most of the difficulties in the way of 
the common theories of the formation of wood, Du Petit 
Thouars, an ingenious French physiologist, who had possessed 
opportunities of examining the growth of vegetation in tro- 
pical countries, constructed a theory, which, although in 
many points similar to the one proposed, but not proved, by 
his countryman, De la Hire, is nevertheless, from the facts 
and illustrations skilfully brought by the French philosopher 
to his aid, to be considered legitimately as his own. The 
attention of Du Petit Thouars appears to have been first 
especially called to the real origin of wood by having re- 
marked, in the Isle of France, that the branches which are 
emitted by the truncheons of Dracaena (with w^hich hedges 
are formed in that colony) root between the rind and old 
wood, forming rays of which the axis of the new shoot is the 
centre. These rays surround the old stem; the lower ones 
at once elongate greatly towards the earth, and the upper 
ones gradually acquire the same direction ; so that at last, as 
they become disentangled from each other, the whole of them 
pass downwards to the soil. Reflecting upon this curious 
fact, and upon a multitude of others, which I have no space 
to detail, he arrived at the conclusion, that it is not merely 
in the property of increasing the species that buds agree with 
seeds, but that they emit roots in like manner ; and that the 
wood and liber are both formed by the downward descent of 
bud-roots, at first nourished by the moisture of the cambium, 
and finally imbedded in the cellular tissue which is the result 
of the organisation of that secretion. That first tendency 
of the embryo, when it has disengaged itself from the seed, 
to send roots downwards and a stem and leaves upwards, and 
to form buds in the axils of the latter, is in like manner 
possessed by the buds themselves ; so that plants increase in 
size by an endless repetition of the same phenomenon. 
Hence a plant is formed of multitudes of buds or fixed 
embryos, each of which has an independent life and action : 
by its elongation upwards forming new branches and con- 
tinuing itself, and by its elongation downwards forming wood 
and bark; which are therefore, in Du Petit Thouars's opinion, 
a mass of roots. 
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