Dear Sir,

Since you have done me the honor of referring in your latest work, “On the Different Forms of Flowers”, p. 301, to certain observations of mine on the irregularity of the distribution of the two forms of Nepeta glechoma, will you kindly allow me to call your attention to an error in your citation? “Kilderry”, not Kilkenny, is merely the name of my father’s residence. The nearest town is Derry. Since the date of my communication to “Nature” I have only been able to find within several miles a solitary hermaphrodite plant of the ground-ivy.¹ It would seem therefore that the female form, which is not at all rare (and its prevalence cannot be due here to any lack of moisture!), must for a very long time have propagated itself solely by root.

Something parallel is presented by Carduus arvensis,² and teaches the danger of overvaluing the efficacy of insects in crossing the flowers of plants growing at not very great distances apart. There are near this two large patches of this thistle, male and female, separated by a distance of much less than a mile, which throughout the summer form a centre of attraction for hosts of insects of many different kinds; yet I have never been able to discover the production of a single seed— If agriculture permitted it, these two patches would probably spread until they meet each other, and their guests would then become useful to the flowers; but at present, while they are so bountifully supplied by the flowers of one patch, they have little temptation to leave it in search of any others— Under the name of “Cirsium arvense, L.” D^r. H. Müller has described (“Befruchtung der Blumen”, p. 387)³ an hermaphrodite species, capable of self fertilisation in the absence of insects. Is there here some confusion of synonymy, or a difference of habit in the same species in the two countries?

Axell again (“Fanerogama Växternas Befruktning”, p. 41, 106) compares the structure of the flowers of Viola palustris to that of V. tricolor. V. palustris of British authors has flowers of the type of V. odorata or canina.⁴

D^r. Müller (“Befruchtung”, p. 399) has remarked that Senecio vulgaris⁵ is scarcely ever visited by insects, but is almost wholly dependent on its self fertility for the production of seed. Once only during bright sunshine I have had the satisfaction of seeing a rank patch of groundsel with its flowers crowded by many species of Diptera and one or two of Hemiptera. Is not this plant also capable of being crossed by other agencies, for instance by the wind striking the flower-heads together, or by animals rubbing against them in passing?

Another example of the need for long continued observation at all hours before pronouncing a flower wholly unattractive to insects is afforded by Oxalis acetosella.⁶ As far as I have yet been able to see, the only regular visitor of this species is a small leaf-cutting bee, which is busy for hardly more than an hour at mid-day: at all other times the flowers seem to be quite neglected.

Hoping you will pardon the liberty I have taken in thus venturing to address you, | I beg leave to subscribe myself | Your most sincere admirer and unworthy disciple | W. E. Hart

Charles Darwin Esq^r