My dear Farrer

You are the man to conquer a Coronilla. I have been looking at the half-dried flowers, & am prepared to swear that you have solved the mystery.¹ The difference in the size of the cells on the calyx under the vexillum right down to the common peduncle² is conspicuous. The flour still adhered to this side. I see little bracteæ or stipules apparently with glandular ends at the base of the calyces. Do these secrete? It seems to me a beautiful case.

When I saw the odd shape of the base of the vexillum I concluded that it must have some meaning, but little dreamt what that was. Now there remains only the one serious point, viz. the separation of the one stamen. I dare say that you are right in that nectar was originally secreted within the staminal tube; but why has not the one stamen long since cohered? The great differences in structure for fertilization within the same genus makes one believe that all such points are very variable. With respect to the non-coherence of the one stamen, do examine some flower-buds at a very early age; for parts which are largely developed are often developed to an unusual degree at a very early age; & it seems to me quite possible that the base of the vexillum (to which the single stamen adheres) might thus be developed & thus keep it separate for a time from the other stamens. The cohering stamens to the right & left of the single one seem to me to be pushed out a little laterally. When you have finished yr observations, you really ought to send an account with a diagram to Nature, recalling yr generalization about the diadelphous structure, & now explaining the exception of coronilla.³

Do add a remark how almost every detail of structure has a meaning when a flower is well examined.⁴

Your observations pleased me so much that I c^d not sit still for $\frac{1}{2}$ an hour, & if Effie⁵ had been here she w^d. have had a good laugh at me—

Please to thank M^r Payne for his remarks, which are of value to me with reference to Mimosa.⁶ I am very much in doubt whether opening the sashes can act by favouring the evaporation of the drops: may not the movement of the leaves shake off the drops or change their places? If M^r Payne remembers any plant which is easily injured by drops I wish he w^d put a drop or two on a leaf on a bright day, & cover the plant with a clean bell glass, & do the same for another plant, but without a bell glass over it, & observe the effects.

Thank you much for wishing to see us again at Abinger⁷ & it is very doubtful whether it will be Coronilla, M^r Payne, the new garden, the children, Effie, or yourself which will give me the most pleasure to see again—

yours most sincerely | Ch. Darwin

It will be curious to note in how many years the rough ground becomes quite uniform in its flora

P.S. One may feel sure that primordially nectar was secreted within the flower & then excreted by the calyx, as in some species of Iris & Orchids. This latter being taken advantage of in Coronilla, would allow of the secretion within the flower ceasing, & as this change was going on in the two secretions, all the parts of the flower would become modified & correlated.—