the other form,
and refrained, from not wishing to trouble you. But I am now sorry
I did, for I have hardly any doubt that L. flavum never seeds in any
garden that I have seen, because one form alone is cultivated by slips.
(735/1. Id est, because, the plant being grown from slips, one form
alone usually occurs in any one garden. It is also arguable that it is
grown by slips because only one form is common, and therefore seedlings
cannot be raised.)

(736/1. The following five letters refer to Darwin's work on "bloom"--a
subject on which he did not live to complete his researches:--

One of his earliest letters on this subject was addressed in August,
1873, to Sir Joseph Hooker (736/2. Published in "Life and Letters,"
III., page 339.):

"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 Darwin wrote to the late Lord Farrer:

"I am now become mad about drops of water injuring leaves. Please ask
Mr. Payne (736/3. Lord 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 hothouse orchids I was cautioned not to wet their
leaves; but I never then thought on the subject."

The next letter, though of later date than some which follow it, is
printed here because it briefly sums his results and serves as guide to
the letters dealing with the subject.)

LETTER 736. TO W. THISELTON-DYER.

(736/4. Published in "Life and Letters," III., page 341.)

Down, September 5th [1877].

One word to thank you. I declare, had it not been for your kindness,
we should have broken down. As it is we have made out clearly that with
some plants (chiefly succulent) the bloom checks evaporati