195 
The History of a Forty Years' Friendship. 
thickness, then it may be that the coagulation that Lepeschkin 
studied does not take place in the surface-layer, but only in the 
underlying mass of the protoplast, and that he and Czapek are not 
dealing with the same structure. 
Nevertheless it seems clear that substances which affect the 
lipoid present, either by their lower surface-tension (Czapek) or by 
absorption into it as narcotics (Lepeschkin) do also affect the 
permeation of water-soluble substances like salts and tannins. It 
seems therefore that there must be a close connection between the 
lipoid and non-lipoid material, and to this necessity the view of a 
chemical union seems most acceptable. How intimate the relation 
may be is indicated by the fact that moderate narcotic doses of 
ether diminish permeability to water and salts, while toxic doses of 
ether increase permeability, as Lepeschkin showed for Pilobolus 
exudation. The differential and variable permeability of the proto¬ 
plast for saline solutions is, however, another chapter of physiology 
and cannot be entered upon in this article. 
SIR JOSEPH HOOKER AND CHARLES DARWIN: 
The History of a Forty Years’ Friendship. 
By A. C. Seward. 
N 1909 the University of Cambridge celebrated the centenary of 
the birth of Charles Darwin and the fiftieth anniversary of 
the publication of the “ Origin of Species.” As a permanent 
memorial of the celebration it was decided to publish a volume of 
essays by British and Foreign men of science “ dealing with the 
different aspects of Darwin’s work in the light of recent contri¬ 
butions to knowledge.” Sir Joseph Dalton Hooker, then in his 
ninety-second year, was invited to contribute an Introductory 
Letter to “ Darwin and Modern Science.” In reply to a request 
from the Editor for such a Prefatory note, Sir Joseph wrote, “The 
wish conveyed in your letter ... that I should contribute a Prefatory 
note to the forthcoming Darwin Memorial volume was both gratifying 
and unexpected, and as an evidence of the personal consideration 
of the Committee of publication I feel more thankful for it than I 
can express. My great doubt is as to whether, in consideration of 
