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Darwin Correspondence Project

To C. H. Blackley   5 July [1873]1

Down, | Beckenham, Kent.

July 5th

Dear Sir

I have read about 23 of your book with much interest.2 The power of pollen in exciting the skin & mucous membrane seems to me an astonishing fact.— Would it not be worth while to kill the pollen by a dry heat rather above the boiling point of water, & see if it retains its injurious properties? But my object in writing now is to say that I imagine that you are not fully aware that plants may be divided into 2 great classes,—those with incoherent pollen & those with coherent pollen.

The former are called by Delpino “anemophilous” plants, as they are fertilized by the wind: & the latter “entomiphilous plants”, as they are fert. by insects.3

Perhaps where grass is cut & dried; some pollen of the entomophilous division may be blown about; but naturally hardly any would thus be blown. Whereas the pollen of Anemophilous plants cannot fail to be largely blown in every direction. In your list the Gramineæ, Cyperaceæ, Amentaceæ, Urticaceæ, some Polygonaceæ & Plantagineæ are the sole Anemophilous plants. The Coniferæ evidently belong to the same class, & lakes in the Tyrol are sometimes coated with the pollen of fir-trees.4

I do not know whether you will care to receive these few hasty remarks.—

With my best respects | I remain | Dear Sir | Yours faithfully | Ch. Darwin

Dr. Burdon Sanderson, who has been here, & to whom I showed your book, was much interested by what he had time to read.5

P.S. I have now read a little more. Your investigations in the upper regions seem to me most ingenious & profoundly interesting. I add one or two trifling remarks

p. 148. I have seen an account of buckets-full of coniferous pollen having been swept off the deck of a ship off the American coast; but I cannot give my reference.6

p. 152. I shd. think grains of pollen, after having forced their contents, through the tubes into the plumose stigmata of grasses, could be easily blown away by a strong wind, & would then consist of mere empty cases7

p. 157. Buckwheat is certainly an entomophilous plant & as it is dimorphic depends on Bees for its perfect fertilisation. The wind wd rarely or never carry away much of its pollen.8


P.S. 2d. Riley (a good observer) says in his “Fifth annual Report of the noxious Insects of Missouri” that near St Louis the ground appeared one day as if sprinkled with sulphur from the quantity of coniferous pollen, which must come from the fir-trees, 400 miles distant, then in flower in the S. States.—9


The year is established by the reference to Blackley 1873.
CD refers to Blackley’s Experimental researches on the causes and nature of catarrhus aestivus (hay-fever or hay-asthma) (Blackley 1873). See letter to C. H. Blackley, 14 June [1873] and n. 2.
See letter from Federico Delpino, 18 June 1873, n. 8, and Cross and self fertilisation, p. 381.
The list appears in Blackley 1873, p. 75. CD underlined the anemophilous plants he mentions in his own copy, now in the Darwin Library–CUL (see Marginalia 1: 59). The family Gramineae (grasses) is now more commonly called Poaceae. Urticaceae is the family of nettles, Polygonaceae is the family of buckwheat and knotweed, and Cyperaceae is the family of sedges. The former order Amentaceae included Salicaceae (willows and poplars), Juglandaceae (walnut and hickory), Betulaceae (birch and alder), and Fagaceae (oak, beech, and chestnut). The family Plantaginaceae contains ribworts. Coniferae is the former order of conifers, which are now the class Pinopsida.
Emma Darwin’s diary (DAR 242) records that John Scott Burdon Sanderson and his wife, Ghetal Burdon Sanderson, visited on 4 July 1873.
CD had mentioned the account of coniferous pollen in his unpublished ‘big book’ on species (Natural selection, pp. 51 and 382), citing the article ‘Yellow showers of pollen’ in the American Journal of Science and Arts 42 (1842): 195–7. Blackley speculated about whether the transport of pollen long distances in the upper atmosphere could explain why patients suffered from hay fever out at sea (Blackley 1873, p. 148).
CD annotated this passage in Blackley 1873 ‘error?’ (see Marginalia 1: 59), taking issue with Blackley’s idea that the granular matter of the pollen-grain escaped into the air before being deposited on the microscope slide.
Blackley explained the increase in hay fever as due in part to the replacement of buckwheat as a common cattle feed by grasses, which produced more and larger pollen.
CD’s lightly annotated copies of Charles Valentine Riley Annual reports on the noxious, beneficial, and other, insects of the State of Missouri (Riley 1869–77) are in the Darwin Library–CUL (see Marginalia 1: 711). The St Louis case is in the 1873 report, p. 86 n.


Comments on CHB’s book [Experimental researches on catarrhus aestivus – hay-fever or hay-asthma (1873)].

Explains that some pollens are wind-blown while others depend on insects for dispersal. Effect of pollen on skin and mucous membrane astonishing. Sends a book [M. Wyman, Autumnal catarrh (1872)].

Letter details

Letter no.
Charles Robert Darwin
Charles Harrison Blackley
Sent from
Source of text
John Hay Library, Brown University (Albert E. Lownes Manuscript Collection, Ms.84.2)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 8965,” accessed on 20 November 2017,

Also published in The Correspondence of Charles Darwin, vol. 21