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Darwin was highly prized, not only as a physiological botanist, but as an excellent cultivator. Mr Isaac Anderson-Henry corresponded with him for many years, and I have perused with much interest and pleasure the excellent and kind replies sent by Darwin. I subjoin extracts from some of these letters:—

"January 20, 1863.— ... I may mention that this past spring I tried again two crosses on Primula, with the same result rather more strongly marked, and that I have gone on now for three generations, breeding them what I call homomorphically, with some curious results, which I shall publish whenever I have time. I have sent a paper on Linum to Linn. Soc.; when it is published I will do myself the pleasure of sending to you a copy, and it will, I should think, be in good time for your experiments. I cannot say how glad I am that you will make some experiments on this subject. It does not absolutely follow, in making a cross between distinct species, that the same rule would follow in the fertility of the pollen. I hope that you will try and mark separately (excluding insects, as you know better than I do the necessity), the two kinds of pollen of one species on the stigma of the other, and see in making hybrids what the difference is in fertility, and in the character of the hybrid seedlings.

"This would be an entirely new field for observation and discovery. You will see in my paper that some species of Linum are not dimorphic, and are self-fertile; and so it is in some other genera.

"You refer to L. rubrum; I am not a botanist, and have called one of the species on which I have experimented

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L. grandiflorum, which is crimson, and not uncommon in flower gardens; I hope I have not made a mistake in name….

"My few crosses in Pelargonium were made to get seed from the central peloric or regular flower (I have got one from peloric flower by pollen of peloric), and this leads me to suggest that it would be very interesting to test fertility of peloric flowers in three ways—peloric pollen on peloric stigma, common pollen on peloric stigma, peloric pollen on common stigma of same species. My object is to discover whether, with change of structure of flower, there is any change in fertility of pollen or of female organs. This might also be tested by trying peloric and common pollen on stigma of distinct species and conversely. I believe there is a peloric and common variety of Tropæolum, and a peloric or upright and common variety of some species of Gloxinia, and medial peloric flowers of Pelargonium, and probably others unknown to me.

"To recur to Linum; if you cross distinct species it would, I think, be advisable to take two dimorphic species, and not one dimorphic and the other self-fertile. I have reason to suspect L. trigynum is dimorphic, but it has not yet flowered with me."

In another letter Darwin says:—[2 May [1863]]

"I do not know whether you have used the microscope much, yet it adds immensely to the interest of all such work as ours, and is indeed indispensable for such work. Experience, however, has fully convinced me that the use of the compound without the simple microscope is absolutely injurious to the progress of natural history (excepting of course with Infusoria). I have as yet found no exception to the rule, that when a man has told me he works with the compound alone, his work is valueless."