Note accompanying MS of part of chapter 11 ["Geographical distribution"] of Natural selection [1975].
CD sorry he had to leave the Hookers abruptly to catch his train.
CD relieved by JDH’s positive response to his MS.
CD continues observations on means of transport.
JDH’s Raoul Island paper [J. Linn. Soc. Lond. (Bot.) 22 (1857): 133–41], showing continuity of vegetation with New Zealand, best evidence yet of continental extension.
CD finds JDH’s objections to a mundane cold period significant, and he endeavours to show how they do not rule out mutability.
He is writing on crossing.
CD encloses letter from Asa Gray, although it is critical of JDH.
Role of struggle in forming species in retreat from advancing glaciers.
CD, attempting to clarify debate, states more of his position. External conditions cause "mere variability". Formation of species due to selection. Relation of an organism to its associates far more important than external conditions.
Sends JDH part of MS for chapter 3 of Natural selection ["Possibility of all organic beings crossing"] to be corrected and returned.
JDH’s report of Podostemon flowering cleistogamously under water in Bengal.
[Copious revision by JDH.]
Questions JDH on separation of sexes in trees in New Zealand flora.
CD is convinced of relation between separation of sexes and tree-habit.
Recent hard blows against crossing theory.
CD long tormented by land molluscs on oceanic islands; found transport possible experimentally.
On the variety of species definitions prevalent among naturalists.
