Dear Sir

In answer to your letter of 25^th Jan, which reached me yesterday, I beg to say that I shall be delighted to undertake the examination you wish.¹ At this moment little can be done it being the beginning of the dry season, & scarcely any Melastomaceae are in flower, but as soon as I find an opportunity I shall attend to your request. We have a large number of Melastomaceae here some 50–60 Species. As far as I can see they are visited by insects of various classes, & only a few minutes ago I found that a sort of bee or humble-bee was very busy in the flowers of Heteronoma diversifolium De C.² which we cultivate here for ornament but which is a native & common in certain localities. It appeared to me that the insect was addressing itself principally to the basal appendices of the anthers, but I shall report later on this & other points when I shall have collected a certain number of facts.

I take this opportunity to send you a few remarks which I have had occasion to make in reading your two latest works, particularly the “British & foreign Orchideae”.³ Perhaps you will not find them altogether out of place from an individual who has made vegetable physiology his principal study for some fifteen years or more. That plants are fertilised by insects, is as evident to every body here as well as in Europe, but it is little imagined in Europe on what scale & to what extent it takes place in these latitudes. Besides the agency of butterflies & moths & bees & wasps we have the immense class of ants which are found everywhere visiting the flowers for some purpose or other. Nearly all fig-trees have their Cynips, which is apparently necessary for the fertilisation of these.⁴ I have never found an insect nor good seeds in Ficus elastica, a native of the old world. Even the higher classes of animals contribute their share in this act, as Humming birds f[or] instance. I am nearly certain that such Plants as Anguria, which have a very viscid & heavy pollen, are principally fertilized by Humming birds.

With regard to Orchids a few facts which I have noted will not be uninteresting to you. We have a few Epidendreae, a Schomburgkia, a Cattleya, & an Epidendron which are hardly ever known to open their flowers, but which nearly always set fruit, which however may drop afterwards. I find on examination, that these are fertilized by ants which creep into the flowers at the base of the sepals. In these cases, as in other Epidendreae the pollinia perform their function in situ, & I believe that it can only explained by the ants carrying the viscosity of the stigma to the pollinia, at least this is the only explanation I can find of the phenomenon.⁵ The pollinia get pulpy without being removed from their bed, & the pollen tubes grow down over the anterior face of the style into the ovarium. I should like to know if there are any Orchids cultivated at Home which do not open. Here it is entirely confined to native species. In other Orchids Ants are also very active some at the bracts, some at the base at the sepals & petals & in the flowers.

The Catasetum I have examined repeatedly before I got your book, since then I have not succeeded getting good observations, the last season having been very unfavorable. The conclusions I have arrived at are rather different from yours, but I shall examine the question again in reference to your opinions.⁶ In my opinion Myanthus barbatus & Catasetum tridentatum are distinct species, which assume both three forms, the female & intermediate form being much alike in the two species, but much smaller in My. barbatus. The so called female form of Catasetum tridentatum is in my opinion a fertile hermaphrodite form, the other the male. I believe that the flower of the former is nearly always fertilized by its own pollinia, which I have repeatedly found in a pulpy state & attached to the opening of the stigma which is hardly large enough to receive the pollinia of the male flower. Fecundation takes place in the female long before it reaches that aromatic state of maturity which attracts the noisy crowd of humble bees which surround it later for days, fighting for some substance or other in the flower. The female flower opens very early, when it is still very small & green, & immediately after the ovarium takes a rapid development. The anther although small is fully developed, the pollen apparently sound, there is a caudicle & gland. The pollinia are found soon after at the entrance of the stigmatic cavity as mentioned already, & in that pulpy state which precedes the emission of pollen tubes in these tribes. I believe that here also fecundation is brought on by ants, which are very active about these flowers.

On the other hand I have repeatedly seen that the male & hermaphrodite flowers are visited by the same species (2 or 3) of Humble bees, & I have also seen the gland & pollinia of the male flowers sticking to the back of them. There are in my opinion mechanical obstacles to their fecundating the hermaphrodite flowers.

These are my results before reading your book, since then I have found nothing contradicting them, but I shall cautiously reexamine the matter, & communicate my results if you wish it. I may mention that the intermediate form between the male & hermaphrodite is (here) rare, & that I have no good observations on it.

In conclusion I beg you will command my services in these matters, if f[or] instance you should like to have some materials in Spirit of wine, I shall be most happy to forward whatever I can get together.

I remain dear Sir | sincerely yours | H Crüger

Ch. Darwin Esq