Down, April 8th [1857].
I now want to ask your opinion, and for facts on a point; and as I shall often want to do this during the next year or two, so let me say, once for all, that you must not take trouble out of mere good nature (of which towards me you have a most abundant stock), but you must consider, in regard to the trouble any question may take, whether you think it worth while--as all loss of time so far lessens your original work--to give me facts to be quoted on your authority in my work.

Do not think I shall be disappointed if you cannot spare time; for already I have profited enormously from your judgment and knowledge.

I earnestly beg you to act as I suggest, and not take trouble solely out of good-nature.
My point is as follows: Harvey gives the case of Fucus varying remarkably, and yet in same way under most different conditions.

D.Don makes same remark in regard to Juncus bufonius in England and India.
Polygala vulgaris has white, red, and blue flowers in Faroe, England, and I think Herbert says in Zante.

Now such cases seem to me very striking, as showing how little relation some variations have to climatal conditions.
Do you think there are many such cases?
Does Oxalis corniculata present exactly the same varieties under very different climates?
How is it with any other British plants in New Zealand, or at the foot of the Himalaya?
Will you think over this and let me hear the result?
One other question: do you remember whether the introduced Sonchus in New Zealand was less, equally, or more common than the aboriginal stock of the same species, where both occurred together?
I forget whether there is any other case parallel with this curious one of the Sonchus...
I have been making good, though slow, progress with my book, for facts have been falling nicely into groups, enlightening each other.
LETTER 57.