STEMS, LEAVES, AND BUDS. 
45 
make a gentle curvature of about 18° downwards and inwards, 
until they nearly reach the centre of the column ; they then 
change their direction, and turn downwards and outwards, 
with a greater obliquity than before, until they have nearly 
reached the external surface of the trunk ; they now descend 
downwards in a line parallel with the axis, until they at last 
get so much ramified as not to be followed further. Lindley, 
as above stated, found the first difficulty in Mold’s statement 
to be this, that the loAver part of the trunk is, as it were, 
obstructed by the Avoody bundles, and must, therefore, un- 
questionably be equally hard. Gardner, however, asserts, 
that the woody bundles of the upper leaves do not descend 
quite down to the bottom, so that the loAver as Avell as the 
upper part thus retain an external hard and an internal soft 
part. Lindley further says, the lower part of the bark must 
be much harder than the upper, because a greater quantity of 
Avoody bundles are there met with. That indeed is the case, 
replies Gardner, and every Brazilian knows it. Lindley 
says, thirdly. The hardness of the external part of the trunks 
of the palms cannot originate in the pressure of a neAV growth 
from the interior towards the exterior, but from a cause 
which would correspond with the production of the heart 
wood in the exogens. Is there such a cause, he asks, in the 
endogens ? Gardner replies. The woody substance in the 
endogens is evidently produced from the leaves, and from 
this it may be inferred, that the same is the case Avith the 
exogens, as Du Petit Thouars has already asserted. The 
only difference appears to be this, that the woody fibres, in 
the exogens, remain between the bark and the last layer of 
wood ; while, in the palms, they turn downwards and inAvards, 
then gradually downwards and outwards, and finally descend 
parallel with the axis. 
The remarks of Mr. Gardner appear to me to be, upon 
the whole, very correct. There is another difference to be 
observed, namely, that the trunk of the palms forms itself 
solely from the leaves, whilst other trunks do so from buds 
from which branches are dcA^eloped. 
Contributions to the Anatomy of the Cactaccee, by M. J . 
437 
