To C. H. Blackley   9 March 1877

An offprint of Blackley’s paper ‘New observations on hay-fever, with new experiments on the quantity of ozone in the atmosphere’ is in DAR 136: 9; delivered in 1876, it was published in 1879 under the title ‘On the methods and the instruments used in investigating the causes of hay-fever’ together with the discussion of the paper before the British Homoepathic Society (Blackley 1879).

In Blackley 1879, pp. 129–31, a method was described for determining the weight of pollen-grains using a balance, microscope, and specially made apparatus. Blackley used this data to determine the weight of pollen required to bring on an attack of hay fever. On p. 133, he cited some of CD’s comments on Blackley 1873 (see Correspondence vol. 21, letter to C. H. Blackley, 5 July [1873]).

In Cross and self fertilisation, pp. 376–7, CD referred to Blackley’s experiments showing that more pollen was released by the anthers in dry conditions than wet (Blackley 1873), and cited other authors who had estimated the number of pollen-grains produced by the dandelion, the peony, Wistaria sinensis, and hibiscus. On pp. 405–6, CD gave the weight of pollen produced by a bulrush plant (Typha latifolia), and referred to Blackley’s experiments showing that there were many more pollen-grains in the higher atmosphere than the lower. CD made notes for this reply on the back of his offprint of Blackley 1879, which is now in DAR 136: 9.

The nature of the preparations has not been identified, but for Blackley’s interest in Drosera (the genus of sundews), see the letter from C. H. Blackley, 18 June 1877. Blackley was interested in CD’s experiments showing the very small amounts of substances that induced physiological action in Drosera, as supporting evidence for his own research on the very small amounts of pollen that could cause hay fever; see Blackley 1882, pp. 608–9.