xii The Botanical Work of Darwin . 
a record of Darwin’s life. But to me the thought is more 
pressingly present, that without Hooker’s constant help his great 
task would not have been carried out on the botanical side. 
Only part of these letters are given in the Life and Letters, 
when the remainder are published they will only heighten 
the impression of the value to science of this memorable 
friendship. It was not merely information, guidance, explana- 
tion, that he received, but an inspiriting companionship, 
a fresh and vigorous influence giving continuous refreshment 
to the solitary worker. 
The following list of subjects, taken at random from my 
father’s letters to Sir Joseph, give an idea of the subjects 
discussed during the evolutionary period : — The dispersal of 
seeds, continental extension, geographical barriers, the arctic 
Flora, alpine plants, large genera varying, coal plants, island 
Floras 1 , aberrant genera, direct action of conditions, rarity 
and extinction, sterility, graft hybrids. Many of these were 
also the subject of correspondence with Asa Gray, H. C. 
Watson, and others, with results familiar to us in the Origin. 
One of the few pieces of his published botanical researches 
made use of in the Origin was his series of experiments on the 
flotation and vitality of seeds in salt water. The chief mass of 
his work on crossing plants was later than 1859, and it will 
be found that in the Origin his material comes chiefly from 
Knight, Kolreuter, and Gartner. 
He used to sneer at himself as a compiler: — ‘The in- 
accuracy of the blessed gang (of which I am one) of compilers 
passes all bounds 1 .’ But ‘ compiling’ in his sense was not an 
easy art, the first requisite being an instinctive power of 
knowing the trustworthy authorities from the untrustworthy. 
In writing to Professor Huxley this was italicized, The 
difficulty is to knovo what to trust. He adds too, ‘ I have 
picked up most by reading really numberless special treatises, 
and all agricultural and horticultural journals ; but it is a 
work of long years. ... I have found it very important asso- 
ciating with fanciers and breeders V 
1 Life and Letters, Vol. ii, p. 281, note. 
2 Ibid., p. 281, 
