CD encloses letter from Asa Gray, although it is critical of JDH.

Role of struggle in forming species in retreat from advancing glaciers.

Continued debate on formation of species as a result of retreat from glaciers.

JDH suggests internal powers of species modification, which he knows CD abhors.

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.

Questions JDH on separation of sexes in trees in New Zealand flora.

Has done New Zealand flora calculations. Results support CD’s theory of necessity of crossing. Trees tend to have separate sexes.

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.

CD finds Alphonse de Candolle very useful, though JDH has low opinion.

CD argues for accidental introductions explaining some odd distributions, e.g., New Zealand vs Australian plants.

CD’s method.

Diverging affinities in isolated genera.

CD will advise W. F. Daniell on collecting.

CD will advise Daniell not to apply for Royal Society grant.

CD’s experiment: fish fed seeds, which germinated when voided.

Separation of sexes in trees [U. S.].

Do plants offer positive evidence for "continuous land" theory?

Protean genera.

Ranges of species in large vs small genera: Asa Gray’s compilation fits CD’s expectation.

CD studies seedling mortality in his weed garden.

JDH’s work on Indian flora.

Independence of variation from climate shown by several plant genera; CD asks for confirmation.

Progressing with book [Natural selection].

JDH cites W. H. Harvey’s observations on Fucus and David Don’s on Juncus as examples of variations that are independent of climate. There are many such cases. Gives his working scheme for categorising variation.

Thanks JDH for response on variation. Studying variations that seem correlated with environment, e.g., north vs south, ascending mountains.

CD’s weed garden: observations on slugs killing seedlings.

Seed-salting. One-seventh of the plants of any country could be transported 924 miles by sea and would germinate.

Curative power of hydropathy.

General hairiness of alpine plants questioned: direct environmental effect.

CD has long felt JDH is too hard on bad observers.

JDH has shaved the hair off the alpine plant.

CD apologises for his criticism.

Apparent but false relations of plant structure to climate: heath-like foliage of all Cape of Good Hope plants.

JDH’s last letter demolishes woolly alpine plant theory.

Correlation of apetalous flowers and cold climate.

Asks JDH’s opinion, and botanical evidence, on important law: parts that are highly developed in comparison to other allied species are very variable.

Interest in hairiness of alpine plants revived by reading A. Moquin-Tandon [Éléments de tératologie végétale (1841)]; correlation with dryness. CD seeks interpretation independent of direct environmental effect.

Qualifications of John Lindley, Huxley, Albany Hancock, Joseph Prestwich, J. C. Ross, and Francis Beaufort for Royal Medal.