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Darwin Correspondence Project

From Richard Spruce   15 April 1869

Welburn. | York.

15. April. 1869.

Dear Sir

I was much obliged for your kind 〈le〉tter & for the suggestions it contained.1 I shd. 〈ha〉ve acknowledged it earlier but that I have been little able to write. I have sought out your letter written many years ago to me about Melastomes. I find it asks for information chiefly about any dimorphism of the sexual organs, such as you have observed in the allied order of Lythraceæ.2

I recollect looking through my notes in vain for any record of such structure. The baccate3 Melastomaceæ, such as I chiefly gathered, have stamens remarkably equable in length, although usually in a double row. The filaments and anthers, white in some, yellow in others, are apt to turn rose and even purple after shedding their pollen, which (in these species) is 〈n〉ever green.

The only observation I have preserved about their fertilisation you will find in my ‘Report on Expedition to procure Red Bark Tree’;4 but as it is unlikely you should have a copy of that Report I will copy it here.

“The first plant which took my attention at Limon,5 〈af〉ter the Cinchona, was a beautiful epiphytal Blakea,6 〈gro〉wing from 12 to 18ft high with large coriaceous 〈lea〉ves & large rose-coloured flowers. At the base of 〈the〉 flower is a turgid involucre, of four large orbicular, widely & closely imbricated leaves, within which is secreted a limpid fluid. When the corolla falls away, the involucral leaves close firm〈ly〉 over the calyx, and do not open out, nor does the contained fluid dry up, until the globose ro〈s〉eate be〈  〉 the size of a pea, is quite ripe. Another singu〈lar〉 character is the syngenesious anthers, with a minu〈te〉 pore at the apex of each cell, through which not a g〈rain〉 of pollen ever escapes, as I satisfied myself by repeated observation; fertilisation being effected through the agency of minute beetles, which abound in the flowers, and eat away the inner edge of the anther-cells—probably part of the pollen also.”

This is what I wrote on the spot, but I have no doubt now that the pollen, liberated by the beetles, falls on the honeyed disk, whence it is carried off by winged insects & deposited on the stigmas of other flowers; for the stigma hangs out far beyond both petals & stamens, therefore out of reach of the pollen as it falls into the centre of the flower.

It is noteworthy that in this most geometrical of of all orders of flowering-plants—for the strongl〈y〉 ribbed leaves, often purple beneath, closely wired with the numerous parallel veins between the ribs, have reminded me of some delicate fabric of copper or cast-iron—the only departure from symmetry is in the style going out between the filaments on one side, so that the stigma becomes quite excentric to the flower   Sometimes the stamens are slightly declinate in the same direction as the style.* I have observed t〈hat〉 flies alighting on the flower use the large pelta〈te〉 stigma as a support for their hind legs whilst poking their noses into the disk. Surely here is an 〈i〉nstance of the effects of direct mechanical action 〈o〉n the part of insects, the style having become declinate through this perpetual “sagging” (as we say in Yorkshire, 〈but a〉s Shakespeare says it too I suppose the word is 〈go〉od English).7

When I have seen flies tugging & poking at the 〈s〉iphon-like corollas of some Gardoquias, Salvias, Siphocampyli, &c.8 I have said to myself “Surely these flowers have become arcuate through the long-continued action of the flies.”

I have not by me your charming book on the Fertilisation of Orchids,9 but I thought you had admitted in part the direct agency of insects in modifying the structure of the flowers. When my paper is printed I will take care not to attribute to you any opinions you do not really hold.

Does not Natural Selection balance all internal & external influences, to the good of the individual, as 〈f〉ar as may be; and when opposing agencies become too strong for it, still keep up the struggle (as it were) to the last gasp?

There are some structures which (so far as we can see) are neither beneficial nor otherwise to plants and animals in their struggle for life. Such may b〈e〉 the sacs on the leaves of Tococas, which perhaps 〈  〉 not have attained to permanence except in a 〈reg〉ion where the climate scarcely varies throughout the year.10

If a gall were always to appear in the same part of a plant—if it could be permanently tenanted—if it cd. be proved not prejudicial but possibly eve〈n〉 beneficial to the plant—I do not see why it shou〈ld〉 not become hereditary.

I have many times seen sacs on Tococa-leaves even full-grown ones—that were imperforate an〈d〉 therefore untenanted by ants: that alone proves t〈he〉sacs to be inherited. I shd. think instances of th〈is〉 might be found on my specimens at Kew.11 I wish 〈I〉 had them here & cd. send you a leaf.

My only doubt is, if the ants really cultivate these sacs, as we cultivate cabbages & turnips, wd. not the saccate leaves become plane even in a few generations?

I do not see what influence the secretions of ants cd. have on the Tococas, except in the way of manure. Dead vegetable tissues are by their action changed to the colour & consistence of tinder, as my carefully put away linen has many times borne witness.

In fine, you must not let my speculations turn you aside from more important matters; but if at any time you think I may be able to furnish information that you require I will most gladly do it to the best of my ability.

I am Dear Sir | Yours very respectfully | Richd. Spruce

Ch. Darwin Esq.

* In Blakea, Bellucia, & other large-flowered genera, but not 〈    〉

CD annotations

1.1 I was … copy it here. 3.3] crossed pencil
6.8 stigma as a … ability. 15.3] crossed pencil
Top of letter: one word illeg, blue crayon; ‘Manner of fert of Melastom.’ pencil

Footnotes

See letter from Richard Spruce, [before 1 April 1869] and n. 2. Spruce refers to the order (now family) Lythraceae. CD had published on Lythrum in his paper ‘Three forms of Lythrum salicaria’.
Baccate: having berries.
Spruce 1861; see also Spruce 1908, 2: 261–310. Spruce spent 1860 in Ecuador, obtaining seeds and young plants of Cinchona succirubra (now C. pubescens; the red bark tree) for the Indian Government. Cinchona was used to produce quinine, an anti-malarial drug. Specimens of the wood of Cinchona are in the Richard Spruce Collection, Royal Botanic Gardens, Kew.
El Limon was a group of small cane farms on the western side of the mountain Chimborazo (Spruce 1908, 2: 259).
Blakea is a genus in the family Melastomataceae.
‘The mind I sway by and the heart I bear | shall never sag with doubt nor shake with fear.’ William Shakespeare, Macbeth, 5.3: 9–10.
Gardoquia is a synonym of Satureja (savory), a member, like Salvia (sage) of the family Lamiaceae. Siphocampylus is a member of the family Campanulaceae.
Orchids.
Spruce refers to the genus Tococa, which he discussed in the paper that he sent to CD (see letter from Richard Spruce, [before 1 April 1869] and n. 3).
Several herbarium specimens of Tococa species collected by Spruce are in the Richard Spruce Collection, Royal Botanic Gardens, Kew. For a database of Spruce’s specimens, see Richard Spruce collection, Natural History Museum, London, 2007, http://www.nhm.ac.uk/jdsml/research-curation/projects/spruce/.

Summary

Describes the floral structure and fertilisation of some melastomes;

discusses the direct agency of insects in modifying the structure of flowers.

Letter details

Letter no.
DCP-LETT-6697
From
Richard Spruce
To
Charles Robert Darwin
Sent from
Welburn, Castle Howard
Source of text
DAR 177: 242
Physical description
4pp damaged †

Please cite as

Darwin Correspondence Project, “Letter no. 6697,” accessed on 24 February 2019, http://www.darwinproject.ac.uk/DCP-LETT-6697

Also published in The Correspondence of Charles Darwin, vol. 17

letter