My dear M^r Thwaites

By an odd chance, two days before receiving your letter of May 15^th I wrote to you on Primula.—²

I am particularly glad to hear of Sethia. Menyanthes is said to be dimorphic like Primula; so I am not surprised at Limnanthemum;³ it will be a curious point to compare Villarsia (I have been blundering, I fancied Villarsia was diœcious.) with Menyanthes, if I can make out any difference in fertility in the two of Menyanthes.⁴ Have you any Malpighiaceæ? if so, I very much wish you would mark the imperfect flowers & see if they set seed.— Also whether they are closed, & whether the pollen-tubes are emitted from the pollen-grains within the anthers & then penetrate the stigma.— This is the case in the imperfect flowers of Viola & Oxalis.—⁵

Many thanks for your Governor’s letter: you do not say whether I am to return it, so I will keep it till I hear.—⁶

In Haste, pray believe me | yours very sincerely | Ch. Darwin—

I suppose it would be too troublesome for you to mark $\frac{1}{2}$ a dozen plants of the two forms Limnanthemum & count the capsules, & compare the produce of seed by weighing or counting.— I suspect the dimorphism of Primula is often, (though not at all necessarily) the high-road to diœciousness.⁷