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The Life and Letters of Darwin, Volume 2

Miscellaneous Botanical Letters
1873-1882.
[The present chapter contains a series of miscellaneous letters on botanical subjects.
Some of them show my father's varied interests in botanical science, and others give
account of researches which never reached completion.]
BLOOM ON LEAVES AND FRUIT.
[His researches into the meaning of the "bloom," or waxy coating found on many leaves,
was one of those inquiries which remained unfinished at the time of his death. He
amassed a quantity of notes on the subject, part of which I hope to publish at no distant
date. (A small instalment on the relation between bloom and the distribution of the
stomata on leaves has appeared in the 'Journal of the Linnean Society,' 1886. Tschirsch
("Linnaea", 1881) has published results identical with some which my father and myself
obtained, viz. that bloom diminishes transpiration. The same fact was previously
published by Garreau in 1850.)
One of his earliest letters on this subject was addressed in August, 1873, to Sir Joseph
Hooker:--
"I want a little information from you, and if you do not yourself know, please to enquire
of some of the wise men of Kew.
"Why are the leaves and fruit of so many plants protected by a thin layer of waxy matter
(like the common cabbage), or with fine hair, so that when such leaves or fruit are
immersed in water they appear as if encased in thin glass? It is really a pretty sight to put
a pod of the common pea, or a raspberry into water. I find several leaves are thus
protected on the under surface and not on the upper.
"How can water injure the leaves if indeed this is at all the case?"
On this latter point he wrote to Sir Thomas Farrer:--
"I am now become mad about drops of water injuring leaves. Please ask Mr. Paine (Sir
Thomas Farrer's gardener.) whether he believes, FROM HIS OWN EXPERIENCE, that
drops of water injure leaves or fruit in his conservatories. It is said that the drops act as
burning-glasses; if this is true, they would not be at all injurious on cloudy days. As he is
so acute a man, I should very much like to hear his opinion. I remember when I grew hot-
house orchids I was cautioned not to wet their leaves; but I never then thought on the
subject.
"I enjoyed my visit greatly with you, and I am very sure that all England could not afford
a kinder and pleasanter host."
 
 
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