Every year when the boughs of a plant [or tree] have made an end of
maturing their growth, they will have made, when put together, a
thickness equal to that of the main stem; and at every stage of its
ramification you will find the thickness of the said main stem; as:
_i k_, _g h_, _e f_, _c d_, _a b_, will always be equal to each
other; unless the tree is pollard--if so the rule does not hold
good.

All the branches have a direction which tends to the centre of the
tree _m_.

[Footnote: The two sketches of leafless trees one above another on
the left hand side of Pl. XXVII, No. 1, belong to this passage.]