in both, but that of the new shoot is, I suppose, chiefly
active in sending down the new wood to thicken the old one, which is
collected, however, and fastened by the extending pith-rays below. You see,
I have given each shoot four fibres of wood for its own; then the four
fibres of the upper one send out two to thicken the lower: the pith-rays,
represented by the white transverse claws, catch and gather all together.
Mind, I certify nothing of this to you; but if this do not happen,--let the
botanists tell you what _does_.

19. Secondly. The wood, represented by these four lines, is to be always
remembered as consisting of fibres and vessels; therefore it is called
'vascular,' a word which you may as well remember (though rarely needed in
familiar English), with its roots, _vas_, a vase, and _vasculum_, a little
vase or phial. 'Vascule' may sometimes be allowed in botanical descriptions
where 'cell' is not clear enough; thus, at present, we find our botanists
calling the pith 'cellular' but the wood 'vascular,' with, I think, the
implied meaning that a 'vascule,' little or large, is a long thing, and has
some liquid in it, while a 'cell' is a more or less round thing, and to be
supposed empty, unless described as full. But what liquid fills the
vascules of the wood, they do not tell us.[44] I assume that they absorb
water, as long as the tree lives.

[Illustration: FIG. 27.]

20. Wood, whether vascular or fibrous, is however formed, in outlaid
plants, first outside of the pith, and then, in shoots of the second year,
outside of the wood of the first, and in the third year, outside of the
wood of the second; so that supposing the quantity of wood sent down from
the growing shoot distributed on a flat plane, the structure in the third
year would be as in Figure 27. But since the new wood is distributed all
round the stem, (in successive cords or threads, if not at once), the
increase of substance after a year or two would be untraceable, unless more
shoots than one were formed at the extremity of the branch. Of actual bud
and branch structure, I gave introductory account long since in the fifth
volume of 'Modern Painters.'[45] to which I would now refer the reader; but
both then, and to-day, after twenty years' further time allowed me, I am
unable to give the least explanation of the mode in which the wood is
really added to the interior stem. I cannot find, even, whether this is
mainly done in springtime, or in the sum