CHAP. 36.—LEAVES WHICH TURN ROUND EVERY YEAR.
We find a most remarkable and, indeed, a marvellous peculiarity[1] existing in the elm, the lime, the olive, the white poplar, and the willow; for immediately after the summer solstice
the leaves of these trees turn completely round; indeed, we
have no sign which indicates with greater certainty that that
period has past.
(24.) These trees also present in their leaves the same difference that is to be observed in those of all the rest: the
underside, which looks towards the ground, is of a green,
grassy colour, and has a smooth surface;[2] while the veins, the
callous skin, and the articulations, lie upon the upper face, the
veins making incisions in the parts beneath, like those to be
seen upon the human hand. The leaf of the olive is whiter
above, and not so smooth; the same is the case, too, with that
of the ivy. The leaves of all trees turn[3] every day towards the sun, the object being that the under side may be
warmed by its heat. The upper surface of them all has a
down upon it, in however small quantity it may be; in some
countries this down is used as a kind of wool.[4]
1. See B. xviii. c. 68, where he enlarges still further on this asserted
peculiarity; he borrows his statement from Theophrastus, Hist. Plant.
B. i. c. 16.
2. These statements are quite conformable with the fact.
3. This statement is quite true, so far as the fact that the leaves have
not the same position in the day-time as during the night: the changes of
position vary greatly, however, in the different kinds. It is generally thought
that an organic irritability is the cause of this phenomenon.
4. This seems to be the meaning of "In aliis gentium lana est." He
alludes, probably, to cotton or silk: see B. vi. c. 20. Thunberg tells us that
at Roodesand, near the Cape of Good Hope, there grows so thick a down
on the Buplevrum giganteum of Lamarck, that it is employed to imitate a
sort of white velvet, and is used for bonnets, gloves, stockings, &c.