A leaf always turns its upper side towards the sky so that it may
the better receive, on all its surface, the dew which drops gently
from the atmosphere. And these leaves are so distributed on the
plant as that one shall cover the other as little as possible, but
shall lie alternately one above another as may be seen in the ivy
which covers the walls. And this alternation serves two ends; that
is, to leave intervals by which the air and sun may penetrate
between them. The 2nd reason is that the drops which fall from the
first leaf may fall onto the fourth or--in other trees--onto the
sixth.