Why a Branch Grows Thickest Below, and the Making of Bark
Moisture sinks to the underside; sap of April turns skin to bark; the mossy north side of old trunks
Continuing on tree structure, this leaf explains that the largest shoots grow on the underside of a great branch, because moisture sinks to the lower side when the sun does not drive it off, thickening the bark there; trees therefore throw many branches downward, and neighbouring plants avoid crowding by giving room to one another. A chapter on bark attributes growth in girth to sap generated in April between the inner skin and the wood, the skin turning to bark and cracking anew. A short chapter observes that the north side of old trunks is clothed in a greenish downy growth, and a further heading on bark follows. The page is a clear Melzi transcription with no drawings.
On this page
Why the underside of a branch grows thickest
The moisture of a branch, when not driven off by the sun's heat, falls back to its underside, where it is most abundant and nourishes most, so the bark and the little shoots are larger below than above. Because trees throw so many branches downward, the branch beneath does not push large shoots against the one above, and neighbouring plants give room to one another rather than crowd.
Bark: the sap of April and its new cracks
The growth in thickness of a plant is made by sap generated in the month of April, between the inner skin and the wood of the tree. At that time the inner skin turns into bark, and the bark gains new cracks within the depths of its ordinary cracks.
Greenish down on the north side of old trunks
The northern side of old trees always clothes the bark of its trunk with a greenish downy growth. The text then opens a further heading on the bark of plants.