You will see in the lower branches of the elder, which puts forth
leaves two and two placed crosswise [at right angles] one above
another, that if the stem rises straight up towards the sky this
order never fails; and its largest leaves are on the thickest part
of the stem and the smallest on the slenderest part, that is towards
the top. But, to return to the lower branches, I say that the leaves
on these are placed on them crosswise like [those on] the upper
branches; and as, by the law of all leaves, they are compelled to
turn their upper surface towards the sky to catch the dew at night,
it is necessary that those so placed should twist round and no
longer form a cross.

[Footnote: See Pl. XXVII, No. 5.]