Ɛpsilon

To G. H. Darwin   8 January [1876]1

Jan 8th

My dear George

I have a great number of measurements like the following imaginary cases.

Crossed Plants Number of plants measured Self-fert. plants number of plants measured Average height
A. species 4 average height 100 ——— 4 —– 90
C. species 17 ———– 100 ——— 16 —– 65
D. species 3 ———– 100 ——— 4 —– 70
34 33

Now what I want to know would it be an easy calculation to give the average or mean height of the 33 self-fertilised plants, the 34 crossed plants being still taken as 100.?2 I shd. rather like to know what the general mean is of all the crossed & self-fertilised plants which I measured; but I want more particularly, because in half-a-dozen cases the self-fertilised plants exceeded in height the crossed, & I desire to know whether this mean excess equals the mean excess of the crossed over the self-fertilised.

But the results wd. not be worth great labour, & I have no idea how it could be done. If the job was simple I could copy out the list & set Mr. Norman3 at the task.

It is a bitter frost here: therm 26o midday & I have been hoping that you are far south & warm.4

Yours affect. C. Darwin

1
The year is established by the period at which CD was at work on the manuscript of Cross and self fertilisation (see n. 2, below).
2
CD’s table of the relative heights of the offspring of crossed and of self-fertilised plants was published in Cross and self fertilisation, pp. 240–3, and included a column for the ratio of the average height of the crossed to the average height of the self-fertilised plants, the former being taken as one hundred. The original notes and calculations are in DAR 76 and DAR 78. There are calculations at the top of this letter by George in preparation for his reply (letter from G. H. Darwin, [after 8 January 1876]). CD started work on the manuscript of Cross and self fertilisation on 3 October 1875 (Correspondence vol. 23, letter to Thomas Meehan, 3 October 1875 and n. 4); the book was published in December 1876 (DAR 210.11: 6).
4
George had been due to visit Bournemouth (letter from Emma Darwin to Leonard Darwin, 20 December [1875] (DAR 239.23: 1.39)).

Manuscript Alterations and Comments

2.9 average] below del ‘av’
3.1 calculation] after del ‘to’
3.3 crossed & self-fertilised 3.4] interl
3.4 because in] ‘in’ interl
4.1 great] after del ‘great’

Please cite as “DCP-LETT-10348,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-10348