More Letters of Charles Darwin Volume I

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The presence of a frog in New Zealand seems to me a strongish fact for
continental connexion, for I assume that sea water would kill spawn, but I
shall try. The spawn, I find, will live about ten days out of water, but I
do not think it could possibly stick to a bird.

What you say about no one realising creation strikes me as very true; but I
think and hope that there is nearly as much difference between trying to
find out whether species of a genus have had a common ancestor and
concerning oneself with the first origin of life, as between making out the
laws of chemical attraction and the first origin of matter.

I thought that Gray's letter had come open to you, and that you had read
it: you will see what I asked--viz., for habitats of the alpine plants,
but I presume there will be nothing new to you. Please return both. How
pleasantly Gray takes my request, and I think I shall have done a good turn
if I make him write a paper on geographical distribution of plants of
United States.

I have written him a very long letter, telling him some of the points about
which I should feel curious. But on my life it is sublimely ridiculous, my
making suggestions to such a man.

I cannot help thinking that what you say about low plants being widely
distributed and standing injurious conditions better than higher ones (but
is not this most difficult to show?) is equally favourable to sea-
transport, to continental connexions, and all other means. Pray do not
suppose that I fancy that if I could show that nearly all seeds could stand
an almost indefinite period of immersion in sea-water, that I have done
more than one EXTREMELY SMALL step in solving the problem of distribution,
for I can quite appreciate the importance of the fact you point out; and
then the directions of currents in past and present times have to be
considered!!

I shall be very curious to hear Berkeley's results in the salting line.

With respect to geological changes, I ought to be one of the last men to
undervalue them after my map of coral islands, and after what I have seen
of elevation on coast of America. Farewell. I hope my letters do not
bother you. Again, and for the last time, I say that I should be extremely
vexed if ever you write to me against the grain or when tired.

LETTER 323. TO J.S HENSLOW.
Down, July 2nd [1855].

Very many thanks for all you have done, and so very kindly promise to do
for me.

Will you make a present to each of the little girls (if not too big and
grandiose) of six pence (for which I send stamps), who are going to collect
seeds for me: viz., Lychnis, white, red, and flesh-colour (if such occur).

...Will you be so kind as to look at them before sent, just to see
positively that they are correct, for remember how ignorant botanically I
am.

Do you see the "Gardeners' Chronicle," and did you notice some little
experiments of mine on salting seeds? Celery and onion seed have come up
after eighty-five days' immersion in the salt water, which seems to me
surprising, and I think throws some light on the wide dispersion of certain
plants. Now, it has occurred to me that it would be an interesting way of
testing the probability of sea-transportal of seeds, to make a list of all
the European plants found in the Azores--a very oceanic archipelago--
collect the seeds, and try if they would stand a pretty long immersion. Do
you think the most able of your little girls would like to collect for me a
packet of seeds of such Azorean plants as grow near Hitcham, I paying, say
3 pence for each packet: it would put a few shillings into their pockets,
and would be an enormous advantage to me, for I grudge the time to collect
the seeds, more especially as I have to learn the plants! The experiment
seems to me worth trying: what do you think? Should you object offering
for me this reward or payment to your little girls? You would have to
select the most conscientious ones, that I might not get wrong seeds. I
have just been comparing the lists, and I suspect you would not have very
many of the Azorean plants. You have, however,

Ranunculus repens,
Ranunculus parviflorus,
Papaver rhoeas,?
Papaver dubium,?
Chelidonium majus,?
Fumaria officinalis.?

All these are Azorean plants.

With respect to cultivating plants, I mean to begin on very few, for I may
find it too troublesome. I have already had for some months primroses and
cowslips, strongly manured with guano, and with flowers picked off, and one
cowslip made to grow in shade; and next spring I shall collect seed.

I think you have quite misunderstood me in regard to my object in getting
you to mark in accompanying list with (x) all the "close species" (323/1.
See Letter 279.) i.e., such as you do not think to be varieties, but which
nevertheless are very closely allied; it has nothing whatever to do with
their cultivation, but I cannot tell you [my] object, as it might
unconsciously influence you in marking them. Will you draw your pencil
right through all the names of those (few) species, of which you may know
nothing. Afterwards, when done, I will tell you my object--not that it is
worth telling, though I myself am very curious on the subject. I know and
can perceive that the definition of "close species" is very vague, and
therefore I should not care for the list being marked by any one, except by
such as yourself.

Forgive this long letter. I thank you heartily for all your assistance.

My dear old Master,
Yours affectionately,
C. Darwin.

Perhaps 3 pence would be hardly enough, and if the number of kinds does not
turn out very great it shall be 6 pence per packet.

LETTER 324. ASA GRAY TO CHARLES DARWIN.

(324/1. In reply to Darwin's letter, June 8th, 1855, given in "Life and
Letters," II., page 61.)

Harvard University, Cambridge, U.S., June 30th, 1855.

Your long letter of the 8th inst. is full of interest to me, and I shall
follow out your hints as far as I can. I rejoice in furnishing facts to
others to work up in their bearing on general questions, and feel it the
more my duty to do so inasmuch as from preoccupation of mind and time and
want of experience I am unable to contribute direct original investigations
of the sort to the advancement of science.

Your request at the close of your letter, which you have such needless
hesitation in making, is just the sort of one which it is easy for me to
reply to, as it lies directly in my way. It would probably pass out of my
mind, however, at the time you propose, so I will attend to it at once, to
fill up the intervals of time left me while attending to one or two pupils.
So I take some unbound sheets of a copy of the "Manual," and mark off the
"close species" by connecting them with a bracket.

Those thus connected, some of them, I should in revision unite under one,
many more Dr. Hooker would unite, and for the rest it would not be
extraordinary if, in any case, the discovery of intermediate forms
compelled their union.

As I have noted on the blank page of the sheets I send you (through Sir
William Hooker), I suppose that if we extended the area, say to that of our
flora of North America, we should find that the proportion of "close
species" to the whole flora increased considerably. But here I speak at a
venture. Some day I will test it for a few families.

If you take for comparison with what I send you, the "British Flora," or
Koch's "Flora Germanica," or Godron's "Flora of France," and mark the
"close species" on the same principle, you will doubtless find a much
greater number. Of course you will not infer from this that the two floras
differ in this respect; since the difference is probably owing to the facts
that (1) there have not been so many observers here bent upon detecting
differences; and (2) our species, thanks mostly to Dr. Torrey and myself,
have been more thoroughly castigated. What stands for one species in the
"Manual" would figure in almost any European flora as two, three, or more,
in a very considerable number of cases.

In boldly reducing nominal species J. Hooker is doing a good work; but his
vocation--like that of any other reformer--exposes him to temptations and
dangers.

Because you have shown that a and b are so connected by intermediate forms
that we cannot do otherwise than regard them as variations of one species,
we may not conclude that c and d, differing much in the same way and to the
same degree, are of one species, before an equal amount of evidence is
actually obtained. That is, when two sets of individuals exhibit any grave
differences, the burden of proof of their common origin lies with the
person who takes that view; and each case must be decided on its own
evidence, and not on analogy, if our conclusions in this way are to be of
real value. Of course we must often jump at conclusions from imperfect
evidence. I should like to write an essay on species some day; but before
I should have time to do it, in my plodding way, I hope you or Hooker will
do it, and much better far. I am most glad to be in conference with Hooker
and yourself on these matters, and I think we may, or rather you may, in a
few years settle the question as to whether Agassiz's or Hooker's views are
correct; they are certainly widely different.

Apropos to this, many thanks for the paper containing your experiments on
seeds exposed to sea water. Why has nobody thought of trying the
experiment before, instead of taking it for granted that salt water kills
seeds? I shall have it nearly all reprinted in "Silliman's Journal" as a
nut for Agassiz to crack.

LETTER 325. TO ASA GRAY.
Down, May 2nd [1856?]

I have received your very kind note of April 8th. In truth it is
preposterous in me to give you hints; but it will give me real pleasure to
write to you just as I talk to Hooker, who says my questions are sometimes
suggestive owing to my comparing the ranges, etc., in different kingdoms of
Nature. I will make no further apologies about my presumption; but will
just tell you (though I am certain there will be VERY little new in what I
suggest and ask) the points on which I am very anxious to hear about. I
forget whether you include Arctic America, but if so, for comparison with
other parts of world, I would exclude the Arctic and Alpine-Arctic, as
belonging to a quite distinct category. When excluding the naturalised, I
think De Candolle must be right in advising the exclusion (giving list) of
plants exclusively found in cultivated land, even when it is not known that
they have been introduced by man. I would give list of temperate plants
(if any) found in Eastern Asia, China, and Japan, and not elsewhere.
Nothing would give me a better idea of the flora of United States than the
proportion of its genera to all the genera which are confined to America;
and the proportion of genera confined to America and Eastern Asia with
Japan; the remaining genera would be common to America and Europe and the
rest of world; I presume it would be impossible to show any especial
affinity in genera, if ever so few, between America and Western Europe.
America might be related to Eastern Asia (always excluding Arctic forms) by
a genus having the same species confined to these two regions; or it might
be related by the genus having different species, the genus itself not
being found elsewhere. The relation of the genera (excluding identical
species) seems to me a most important element in geographical distribution
often ignored, and I presume of more difficult application in plants than
in animals, owing to the wider ranges of plants; but I find in New Zealand
(from Hooker) that the consideration of genera with representative species
tells the story of relationship even plainer than the identity of the
species with the different parts of the world. I should like to see the
genera of the United States, say 500 (excluding Arctic and Alpine) divided
into three classes, with the proportions given thus:--

100/500 American genera;

200/500 Old World genera, but not having any identical species in common;

200/500 Old World genera, but having some identical species in common;

Supposing that these 200 genera included 600 U.S. plants, then the 600
would be the denominator to the fraction of the species common to the Old
World. But I am running on at a foolish length.

There is an interesting discussion in De Candolle (about pages 503-514) on
the relation of the size of families to the average range of the individual
species; I cannot but think, from some facts which I collected long before
De Candolle appeared, that he is on wrong scent in having taken families
(owing to their including too great a diversity in the constitution of the
species), but that if he had taken genera, he would have found that the
individual species in large genera range over a greater area than do the
species in small genera: I think if you have materials that this would be
well worth working out, for it is a very singular relation.

With respect to naturalised plants: are any social with you, which are not
so in their parent country? I am surprised that the importance of this has
not more struck De Candolle. Of these naturalised plants are any or many
more variable in your opinion than the average of your United States
plants? I am aware how very vague this must be; but De Candolle has stated
that the naturalised plants do not present varieties; but being very
variable and presenting distinct varieties seems to me rather a different
case: if you would kindly take the trouble to answer this question I
should be very much obliged, whether or no you will enter on such points in
your essay.

With respect to such plants, which have their southern limits within your
area, are the individuals ever or often stunted in their growth or
unhealthy? I have in vain endeavoured to find any botanist who has
observed this point; but I have seen some remarks by Barton on the trees in
United States. Trees seem in this respect to behave rather differently
from other plants.

It would be a very curious point, but I fear you would think it out of your
essay, to compare the list of European plants in Tierra del Fuego (in
Hooker) with those in North America; for, without multiple creation, I
think we must admit that all now in T. del Fuego must have travelled
through North America, and so far they do concern you.

The discussion on social plants (vague as the terms and facts are) in De
Candolle strikes me as the best which I have ever seen: two points strike
me as eminently remarkable in them; that they should ever be social close
to their extreme limits; and secondly, that species having an extremely
confined range, yet should be social where they do occur: I should be
infinitely obliged for any cases either by letter or publicly on these
heads, more especially in regard to a species remaining or ceasing to be
social on the confines of its range.

There is one other point on which I individually should be extremely much
obliged, if you could spare the time to think a little bit and inform me:
viz., whether there are any cases of the same species being more variable
in United States than in other countries in which it is found, or in
different parts of the United States? Wahlenberg says generally that the
same species in going south become more variable than in extreme north.
Even still more am I anxious to know whether any of the genera, which have
most of their species horribly variable (as Rubus or Hieracium are) in
Europe, or other parts of the world, are less variable in the United
States; or, the reverse case, whether you have any odious genera with you
which are less odious in other countries? Any information on this head
would be a real kindness to me.

I suppose your flora is too great; but a simple list in close columns in
small type of all the species, genera, and families, each consecutively
numbered, has always struck me as most useful; and Hooker regrets that he
did not give such list in introduction to New Zealand and other Flora. I
am sure I have given you a larger dose of questions than you bargained for,
and I have kept my word and treated you just as I do Hooker. Nevertheless,
if anything occurs to me during the next two months, I will write freely,
believing that you will forgive me and not think me very presumptuous.

How well De Candolle shows the necessity of comparing nearly equal areas
for proportion of families!

I have re-read this letter, and it is really not worth sending, except for
my own sake. I see I forgot, in beginning, to state that it appeared to me
that the six heads of your Essay included almost every point which could be
desired, and therefore that I had little to say.

LETTER 326. TO J.D. HOOKER.

(326/1. On July 5th, 1856, Darwin wrote to Sir J.D. Hooker:--

"I am going mad and am in despair over your confounded Antarctic island
flora. Will you read over the Tristan list, and see if my remarks on it
are at all accurate. I cannot make out why you consider the vegetation so
Fuegian.")

Down, 8th [July, 1856].

I do hope that this note may arrive in time to save you trouble in one
respect. I am perfectly ashamed of myself, for I find in introduction to
Flora of Fuegia (326/2. "Flora Antarctica," page 216. "Though only 1,000
miles distant from the Cape of Good Hope, and 3,000 from the Strait of
Magalhaens, the botany of this island [Tristan d'Acunha] is far more
intimately allied to that of Fuegia than Africa." Hooker goes on to say
that only Phylica and Pelargonium are Cape forms, while seven species, or
one-quarter of the flora, "are either natives of Fuegia or typical of South
American botany, and the ferns and Lycopodia exhibit a still stronger
affinity.") a short discussion on Tristan plants, which though scored [i.e.
marked in pencil] I had quite forgotten at the time, and had thought only
of looking into introduction to New Zealand Flora. It was very stupid of
me. In my sketch I am forced to pick out the most striking cases of
species which favour the multiple creation doctrine, without indeed great
continental extensions are admitted. Of the many wonderful cases in your
books, the one which strikes me most is that list of species, which you
made for me, common to New Zealand and America, and confined to southern
hemisphere; and in this list those common to Chile and New Zealand seem to
me the most wondrous. I have copied these out and enclosed them. Now I
will promise to ask no more questions, if you will tell me a little about
these. What I want to know is, whether any or many of them are mountain
plants of Chile, so as to bring them in some degree (like the Chonos
plants) under the same category with the Fuegian plants? I see that all
the genera (Edwardsia even having Sandwich Island and Indian species) are
wide-ranging genera, except Myosurus, which seems extra wonderful. Do any
of these genera cling to seaside? Are the other species of these genera
wide rangers? Do be a good Christian and not hate me.

I began last night to re-read your Galapagos paper, and to my taste it is
quite admirable: I see in it some of the points which I thought best in A.
De Candolle! Such is my memory.

Lyell will not express any opinion on continental extensions. (326/3. See
Letters 47, 48.)

LETTER 327. TO C. LYELL.
Down, July 8th [1856].

Very many thanks for your two notes, and especially for Maury's map: also
for books which you are going to lend me.

I am sorry you cannot give any verdict on continental extensions; and I
infer that you think my argument of not much weight against such
extensions; I know I wish I could believe. (327/1. This paragraph is
published in the "Life and Letters," II., page 78; it refers to a letter
(June 25th, 1856, "Life and Letters," II., page 74) giving Darwin's
arguments against the doctrine of "Continental Extension." See Letters 47,
48.)

I have been having a look at Maury (which I once before looked at), and in
respect to Madeira & Co. I must say, that the chart seems to me against
land-extension explaining the introduction of organic beings. Madeira, the
Canaries and Azores are so tied together, that I should have thought they
ought to have been connected by some bank, if changes of level had been
connected with their organic relation. The Azores ought, too, to have
shown more connection with America. I had sometimes speculated whether
icebergs could account for the greater number of European plants and their
more northern character on the Azores, compared with Madeira; but it seems
dangerous until boulders are found there. (327/2. See "Life and Letters,"
II., page 112, for a letter (April 26th, 1858) in which Darwin exults over
the discovery of boulders on the Azores and the fulfilment of the prophecy,
which he was characteristically half inclined to ascribe to Lyell.)

One of the more curious points in Maury is, as it strikes me, in the little
change which about 9,000 feet of sudden elevation would make in the
continent visible, and what a prodigious change 9,000 feet subsidence would
make! Is the difference due to denudation during elevation? Certainly
12,000 feet elevation would make a prodigious change. I have just been
quoting you in my essay on ice carrying seeds in the southern hemisphere,
but this will not do in all the cases. I have had a week of such hard
labour in getting up the relations of all the Antarctic flora from Hooker's
admirable works. Oddly enough, I have just finished in great detail,
giving evidence of coolness in tropical regions during the Glacial epoch,
and the consequent migration of organisms through the tropics. There are a
good many difficulties, but upon the whole it explains much. This has been
a favourite notion with me, almost since I wrote on erratic boulders of the
south. It harmonises with the modification of species; and without
admitting this awful postulate, the Glacial epoch in the south and tropics
does not work in well. About Atlantis, I doubt whether the Canary Islands
are as much more related to the continent as they ought to be, if formerly
connected by continuous land.

Hooker, with whom I have formerly discussed the notion of the world or
great belts of it having been cooler, though he at first saw great
difficulties (and difficulties there are great enough), I think is much
inclined to adopt the idea. With modification of specific forms it
explains some wondrous odd facts in distribution.

But I shall never stop if I get on this subject, on which I have been at
work, sometimes in triumph, sometimes in despair, for the last month.

LETTER 328. ASA GRAY TO CHARLES DARWIN.
Received August 20th, 1856.

I enclose you a proof of the last page, that you may see what our flora
amounts to. The genera of the Cryptogams (Ferns down to Hepaticae) are
illustrated in fourteen crowded plates. So that the volume has become
rather formidable as a class-book, which it is intended for.

I have revised the last proofs to-day. The publishers will bring it out
some time in August. Meanwhile, I am going to have a little holiday, which
I have earned, little as I can spare the time for it. And my wife and I
start on Friday to visit my mother and friends in West New York, and on our
way back I will look in upon the scientific meeting at Albany on the 20th
inst., or later, just to meet some old friends there.

Why could not you come over, on the urgent invitation given to European
savans--and free passage provided back and forth in the steamers? Yet I
believe nobody is coming. Will you not come next year, if a special
invitation is sent you on the same terms?

Boott lately sent me your photograph, which (though not a very perfect one)
I am well pleased to have...

But there is another question in your last letter--one about which a person
can only give an impression--and my impression is that, speaking of plants
of a well-known flora, what we call intermediate varieties are generally
less numerous in individuals than the two states which they connect. That
this would be the case in a flora where things are put as they naturally
should be, I do not much doubt; and the wider are your views about species
(say, for instance, with Dr. Hooker's very latitudinarian notions) the more
plainly would this appear. But practically two things stand hugely in the
way of any application of the fact or principle, if such it be. 1. Our
choice of what to take as the typical forms very often is not free. We
take, e.g., for one of them the particular form of which Linnaeus, say,
happened to have a specimen sent him, and on which [he] established the
species; and I know more than one case in which that is a rare form of a
common species; the other variety will perhaps be the opposite extreme--
whether the most common or not, or will be what L. or [illegible] described
as a 2nd species. Here various intermediate forms may be the most
abundant. 2. It is just the same thing now, in respect to specimens
coming in from our new western country. The form which first comes, and is
described and named, determines the specific character, and this long
sticks as the type, though in fact it may be far from the most common form.
Yet of plants very well known in all their aspects, I can think of several
of which we recognise two leading forms, and rarely see anything really
intermediate, such as our Mentha borealis, its hairy and its smooth
varieties.