492 THE MAKING OF THE ' OEIGIN ' 
Eeally I do not know how to thank you half for all you 
have done for and sent to me. I might with truth do so for 
every single paragraph in your letter and every one volume. 
. . . Your remarks are exactly the thing, which ever since 
being in Tierra del Fuego, I have felt a keen curiosity about, 
and have often complained to Henslow how rarely I could 
find any such general remarks in Botanical works. 
And in 1845 the prospective break in their personal inter- 
course, if Hooker were elected to the chair at Edinburgh, 
is a heavy disappointment to me ; and in a mere selfish point 
of view, as aiding me in my work, your loss is indeed irrepar- 
able. ... I assure you dehberately that I consider all the 
assistance which you have given me is more than I have 
received from an^^one else, and is beyond valuing in my 
eyes. 
More than this : they can express themselves with anima- 
tion to each other, without risk of being misunderstood. 
Hooker contributes much from his own knowledge. Dis- 
tribution is his favourite subject, and he supplies statistics 
in the form desired to show range and migration, struggle 
and sm-vival, from the Floras of the Southern Hemisphere or 
India or the Polar regions, all of which have fallen within his 
dii-ect research. Moreover, he is particularly able to tell 
much about variation, for, as the preceding chapters show, 
he had long been struck by the incertitude of botanists 
on this head, and comparing detailed results'; all over the 
vast fields he had covered, had found "many species as de- 
fined by local observers to be but varieties of a common 
species with every intermediate gradation. He can put 
Darwin in the way of answering the question whether large 
genera with wide ranging species, as should be the case with 
strong and increasing kinds, produce more varieties than 
smaller groups. At the same time he adds a warning as to 
the different impression of distinctness made on botanists by 
a given degree of difference occurring within the large or small 
group, so that what here would be ranked as a variety, would 
there be ranked as a species, to the confusion of any statistics 
