Muller's work on. -and heterostyled plants. -rarity of natural. -J. Scott's work on. -tendency to reversion.

Hydra, sexuality of.

Hydropathy, Darwin and.

Hydrozoa, alternation of generations in.

Hymenoptera, affinities of. -H. Muller on.

Hypericum perforatum, a social plant in U.S.A.

Hyracotherium cuniculus, Owen on.

Iberis, mucus in seeds of.

Ice, as agent in dispersal of boulders. -agent in dispersal of plants. -Forbes on transport by. -agent in lake-formation. -cleavage in. -work of, a new factor in geology.

Ice-action, on land and sea.

Icebergs, as factor in explaining European plants in Azores. -Croll on action of. -Darwin on. -evidence in S. America of. -Hopkins on action of.

Ice-cap, of Arctic regions.

Iceland, importance of records of volcanic phenomena in.

Ignorance, Darwin on immensity of man's.

Ilkley, Darwin's visit to.

Illegitimate offspring, need for repetition of Darwin's experiments on plants'.

Imatophyllum.

Immortality, Darwin on.

Immutability of species. -Falconer disbelieves in. -Darwin on.

Imperfection of the Geological Record, see Geological Record.

Impotence in plants. -see also Self-sterility.

India, British rule in. -flora of. -Hooker in. -varieties of domestic animals in. -H.F. Blanford on. -Darwin on origin of lakes in. -evidence of colder climate in. -J. Scott accepts post in.

Infants, Mrs. E Talbot on development of mind in. -observations on ears of.

Infusoria, possible occurrence in underclays of coal.

Inglis, Sir R., Darwin at breakfast party.

Inheritance, atavism and. -conservative tendency of long. -Hackel on. -hypothesis on. -Jager on. -and Natural Selection. -power of. -J.C. Prichard on. -and variability. -Darwin on. -Galton on.

Insanity, concealment of.

"Insect Life," Howard's.

Insectivorous plants, Darwin's work on.

Insects, alpine. -Lord Avebury on. -Bates on. -fossil. -luminous. -of Madeira. -F. Muller on metamorphosis of. -Sharp's book on. -study of habits more valuable than description of new species. -wingless. -Wollaston on. -antiquity of stridulating organs in. -colour and Sexual Selection. -H. Muller's work on adaptation to fertilisation of flowers. -metamorphosis of. -music as attraction to. -observation on fertilisation of flowers by. -Ramsay on. -Riley's work on. -tropical climate and colours of.

Instinct, Darwin and. -in nest-making. -selection of varying.

Insular floras. -Hooker's lecture on.

Insular forms, in Galapagos, Canaries and Madeira. -beaten by continental forms.

Intelligence, meaning of. -Romanes on Animal. -in worms.

Intercrossing, in pigeons. -Darwin on effects of. -and sterility.

Interglacial periods, Darwin on evidence for.

Intermediate forms. -Bates' paper on. -S. American types as. -crossing and frequent absence of. -extinction of. -Falconer on existence of. -as fossils. -Asa Gray on. -Plagiaulax as evidence of. -Wollaston on rarity in insects.

Introduced plants, Sonchus in New Zealand as example of. -in N. America and Australia. -variability of. -Darwin on.

Introductory Essay to Tasmanian "Flora," Hooker's.

Ipswich, British Association meeting (1851).

Iquique, nitrate of soda beds at.

Ireland, Spanish plants in.

Iris, flowers of. -nectar secretion of.

Islands, comparison between species of rising and sinking. -fauna of. -introduction of plants. -products of. -plants with irregular flowers on. -subsidence of coral. -survival of ancient forms in. -volcanic. -comparison of age of continents and. -former greater extension of.

"Island Life," Darwin's criticism of Wallace's.

Isle of Wight, occurrence of Bee-orchis in.

Isnardia palustris, range of.

Isolation, Bentham underestimates importance of. -Darwin's opinion of. -importance of. -Wagner exaggerates importance of. -Weismann on effects of.

Itajahy, F. Muller's narrow escape from flood of.

Italy, flora of.

Ivy, difference in growth of flowering and creeping branches.

Jaeger, G., letter to. -on pangenesis and inheritance.

Charles Darwin

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