My dear Sir.

The last French Steamer brought me your two letters of Feb. 7 and 22, for which I am much obliged to you.¹

As to your question about the sexual differences of lower animals, I can hardly give you any information.² Among higher Crustacea I know of only one instance of males distinguished by bright colours from their modest females.

In a little Gelasimus of our coast the posterior half of the cephalothorax assumes often, in the adult male, a pure white colour. This white colour may, in a few minutes, change into dirty grey or even black, while at the same time the colours of the anterior half lose much of their brilliancy. The cephalothorax of the female is commonly of a nearly uniform greyish brown. This little gelasimus uses to run about in the sunshine and so is more able to exhibit its beauty to the female than are most other Crustaceans. The number of the males seems to be much larger than that of the females; just now, when I went to catch some specimens, I found a dozen males and only two females. I suspect, that the large pincers may serve to this and perhaps to some other male crabs for fighting for the female; at least, when several males are emprisoned in a glass, they often kill or mutilate each other.—³ Among lower Crustaceans some species of Sapphirina Thomps. offer a most interesting case in point. The males are known since the time of Cook for the brilliancy of their colours, while the females are colourless according to Gegenbaur and Claus. In these little Copepods also the colours are changing (See the enclosed extract from Claus’ book.).—⁴ From Gerstäcker’s Textbook of Zoology I see that the males of some spiders (Sparassus smaragdulus &c) are distinguished by different and more gaudy colours.—⁵ Among Annelids some Syllideæ with alternate generations show very marked sexual differences, so great, that the asexual form, the male and the female were placed in three distinct genera (Autolytus Grube, Diploceræa Gr. and Sacconereis J. Müll.)⁶ Some of the sexual forms have very large eyes and I have found some of these little worms having much prettier colours than is usual with Annelids. Perhaps these colours here also may be due to sexual selection.—

As to the expression of countenance of Negros, I shall keep the subject before my mind and may perhaps be able to answer some of your questions; but I have here no opportunity of observing native S. Americans.⁷

Oncidium flexuosum is a native of our district, and so are the other Orchids of my garden, all of which I collected either on our island or on the neighbouring part of the continent.⁸

I but once saw ramifying filaments of a parasitic cryptogam causing the decay of Orchid-pollen, when I had placed old pollen-masses of Lælia purpurata on the stigma of Brassavola fragrans.— In the case of self-impotent Vandeæ I never saw a trace of cryptogams, which might be considered as the cause of the decay.—⁹

To the list of self-impotent Orchids, in which pollen and stigma of the same plant are poisonous to each other, I can add a small Oncidium (probably undescribed) from Theresopolis¹⁰ in which own pollen after three days’ stay in the stigmatic chamber was decayed and dark brown. This Oncidium grows in company of O. unicorne and though the flowers, as you see, are quite different, (belonging even to a different section of the genus), the pseudobulbs and leaves of the two species are almost undistinguishable. Perhaps this strange ressemblance may be due to mimicry.— I am now experimenting on the last (as to its flower-time), but not least of our Oncidia, the Oncidium crispum, which seems to be an exception among our other self-impotent species of that genus; at least own pollen, placed on the stigma March 23, I found to be quite fresh as well as the stigma and pollen-tubes, when I examined a flower this morning.¹¹

As to the fertility of Epidendrum cinnabarinum being much lessened by self-fertilization, I can now give you one more striking case. I fertilized (Jan. 17) six flowers of a raceme with pollen of the same flowers and obtained six pods, the seeds of which weighed: 1.5— 2.— 1.5— 2.— 2,5— 2.5 grains; most of the seeds were bad.— On the same day I fertilized six flowers of a second raceme of the same plant with pollen of a distinct plant and obtained 5 pods, the seeds of which weighed 5.— 6.— 5.— 5.—5 grains, but few seeds being bad.—¹²

At reading D^r Hildebrand’s paper on Corydalis cava, which you have been so kind as to send me, I was struck by the circumstance that among the 29 seed-capsules obtained by crossing distinct plants, the seeds of which were counted, none had 4 seeds, while about half the number had from 5 to 7, and the other only from 1 to 3 seeds. May not this species be functionally dimorphic, the poor seed-capsules being the result of illegitimate unions?—¹³

⁠⟨⁠Drawing or specimen excised⁠⟩⁠

Here is another dimorphic Rubiacea;¹⁴ the pollen-grains of the short-styled plant are larger (about $\frac{1}{12}$ ^mm diam.), than those of the long-styled (about $\frac{1}{16}$ ^mm diam.). The plant has beautiful blue Fruits.

During the last months I have been making some experiments on the crossing of different species of Orchids; and I hope that these experiments, if continued on a larger scale, will lead to some interesting results. Some points may already be worth mentioning. It seems that much more widely distinct species of Orchids may be successfully crossed, than is usual with plants. Thus I have (as yet unripe) pods of Cattleya elatior var Leopoldi ♀ and Lælia purpurata ♂;—of Cattleya elatior var Russelliana, ♀, and Epidendrum cinnabarinum ♂;—of Brassavola fragrans Lem. ♀ and different species of Epidendrum ♂;—of Oncidium flexuosum ♀ and Cyrtopodium (Andersoni?) ♂;—of Notylia ♀ and Ornithocephalus ♂!—of Sigmatostalix ♀ and Ornithocephalus ♂!—of the small Oncidium from Theresopolis ♀ and Sigmatostalix ♂;—of Oncidium flexuosum ♀ and Gomesa ♂;—of Gomesa ♀ and Onc. flexuosum ♂ etc.—

But the case, which most surprised me, is the following: A Frenchman, Mr. Gautier,¹⁵ bade me to cross for him, in his garden, Zygopetalum maxillare and Miltonia cereola. I did so, without expecting any result; but both the species have now fine swelling pods!— There appears to be no close systematic affinity between the two genera; at least Miltonia is much more closely allied to Oncidium than to Zygopetalum. Mr. Reichenbach even cancels the genus Miltonia, uniting it with Oncidium;¹⁶ but I repeatedly fertilized several species of Oncidium with pollen of Miltonia, without obtaining a single pod.— The only point in which Zygopetalum maxillare and Miltonia cereola closely ressemble each other is the colour of the labellum!—

March 6, when I was fertilizing a Cattleya (probably a var. of C. elatior) with pollen of some other species of the genus and of Epidendrum, I had just at hand some pollinia of Oncidium micropogon and placed them on the stigma of one of the flowers of the Cattleya. Now this flower withered sooner than the other fertilized flowers, and has yielded a fine pod, which is now 36^mm long, while the other pods are about 46^mm long. Probably the pollen-tubes of Oncidium will not be able to fertilize the ovules of Cattleya and I think the pod will wither, when the time of fertilization arrives, but even so the case is curious.— If horticulturists contrived to raise Orchids from seeds, this facility with which widely distant species are crossed, would be a highly valuable quality.—

There is with Orchids the same unaccountable ⁠⟨⁠one-third line excised⁠⟩⁠ fertility of reciprocal crosses, as with other ⁠⟨⁠one-third line excised⁠⟩⁠ certain species seems to have a great fertilizing ⁠⟨⁠one-third line excised⁠⟩⁠ Epidendrum cinnabarinum, these same species are ⁠⟨⁠one-third line excised⁠⟩⁠ with difficulty. I fertilized with pollen of ⁠⟨⁠one-third line excised⁠⟩⁠

Epidendrum Zebra n. sp?¹⁷ 6 flowers, ⁠⟨⁠    ⁠⟩⁠

— fragrans 2 ⁠⟨⁠    ⁠⟩⁠

— raniferum? 2 1.

— vesicatum 2 2

Cattleya elatior 2 1.

Brassavola fragrans. 4. 3.

18 13.

On the other hand I fertilized Epidendrum cinnabarinum with pollen of

Epidendrum Zebra 17 flowers, which yielded 0 pod

— fragrans 4 0.—

— raniferum 37 1 —

— vesicatum 6 0.—

Cattleya elatior 2. 0.

Brassavola fragrans 16. 0.

82 1.

The easity, with which fertilisation is effected and the number of seeds produced is not proportional. Epidendrum Zebra is easily fertilized with Ep. cinnabarinum, but the pods (not yet ripe) will be very poor. On the contrary 14 flowers of Epid. cinnabarinum fertilized with pollen of Ep. Schomburgkii(?) yielded only two pods, but one of these had more seeds than any pod fertilized with pollen of the own species, and also the other was very rich.—

The sterile unions between different species behave in most cases very differently from those of the self-impotent species. First discolours and withers the pedicel of the germen and this discolouring goes slowly on in an upwards direction and even, when the germen falls off, pollen and stigma are generally quite fresh. Generally the germen will fall off 1 or 2 weeks after fertilization; but a germen of Cirrhæa dependens? fertilized with Stanhopea Jan. 24 fell off only March 11; stigma, pollen and pollen tubes were fresh.— Sometimes the pollen grows brownish; but then this discolouring generally begins at the outer surface of the pollen masses, and but in very few cases at the inner surface, where it touches the stigma, whilst the latter is invariably the case, when a self-impotent Oncidium, Gomesa, Sigmatostalix or Notylia is fertilized with own pollen.—¹⁸

Hoping that this letter will find you in good health, Believe me, dear Sir, | very truly and respectfully yours | D^r Fritz Müller.

P.S. I forgot to thank you for the copies of my paper on Climbing plants.¹⁹