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Letter 2770

Darwin, C. R. to Hooker, J. D.

27 Apr [1860]

    Summary Add

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    Sends list of plants with asymmetry in nectar-secreting surfaces and pistils bent in that direction. Shows insect agency so important that structure has changed. Asks for contrary or confirming examples and that request be passed on to Daniel Oliver.

Transcription

[Down]

Ap. 27th

My dear Hooker

Will you run your eye over other side & then tear up or keep as you like.— What I want are facts to upset this apparent rule or (which of course wd please me most) any strong cases to support it. Any one species in a group, with nectar-secreting surface on one side of flower with pistil bent towards that side, wd be, I shd. think, good case.— Do you think Mr Oliver would keep & decipher my miserable notes, & observe a few flowers for me this summer.— Why I care about it, is that it shows that visits of insects are so important, that these visits have led to changed structure.

C. D.

Leguminosæ; in vast number of species pistil bent rectangularly upwards & Bees get nectar at base of standard; but in Kidney-Bean & garden Lathyrus, they always alight on left-hand petal & the stigma by curving points to this same side.

Mem. case of Corydalis & Dielytra alluded to, & Fraxinella—

Alstrœ meria (common orange-flowered kind) 2 upper petals secrete honey, & the pistil is bent up to this side

Gladiolus (orange) much honey on lower side of flower, where the filaments are attached; pistil when mature bends down to this lower side

Delphinus grandiflorus, pistil bent rectangularly so that stigma lies in gangway to nectary. (contrast with columbine)

Tropæolum, stigma when mature slightly bent into gangway

Several Scrophulariaceæ, as Antirrhinum & Pedicularis; some Labiatæ, as the fine Blue Salvia have pistils more or less bent into gangway to nectary

Lobelia fulgens stigma slightly bent down towards gangway

Polygala (common English species) has pistil directed at right angles to where Bees suck the flower

Rhododendron, Viola tricolor, Horse-chesnut all have pistils more or less bent in same manner, ie in path which Bees must brush over in sucking the nectar

C. Darwin

    Footnotes Add

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    f1 2770.f1
    The year is given by the relationship to the preceding letter.
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    f2 2770.f2
    Daniel Oliver was an assistant in the herbarium of the Royal Botanic Gardens, Kew.
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    f3 2770.f3
    None of these plants is included in the discussion `On the relation between the structure and conspicuousness of flowers, the visits of insects, and the advantages of cross-fertilization' in Cross and self fertilisation, pp. 383--4.
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