From Fritz Müller 2 June 1867
June 2d | 1867.
My dear Sir
Your two kind letters of March 25th and Apr. 22d arrived here a few days ago and at the same time the copies of the paper on climbing plants despatched Apr. 20th. I already told you, I think, that the formerly despatched copies also, after an unusual delay, reached me safely.1 Many thanks for all the pain, you have taken.
I must to-day begin with correcting an error of a former letter; the Rubiaceous plant, which I sent you under the name of Diodia, does not belong to that genus, but is a Borreria, as I now see on examining ripe fruits.2 Some species of Diodia, which I observed, are monomorphic. Here is one more dimorphic Rubiaceous plant, 〈specimen excised〉a Coccocypselum; I found no appreciable difference in the size of the pollen-grains of the two forms.3 I enclose seeds of two species of that genus; having as yet seen only a single flowering plant of the second species, I do not know, whether it is dimorphic, though I hardly doubt that it will be so.4 The plants are worth cultivating for their very pretty blue fruits.— Have you ever seen a Danais? I suspect that this Rubiacea also will prove to be dimorphic; Endlicher (gen. plant. no 3267) says it is dioecious, the male (short-styled?) flower having exserted stamens and enclosed styli, whilst in the female (long-styled?) flower the stamens are said to be enclosed and the styli exserted.—5
I must correct also my statements on the curious terrestrial Orchid, of which I told you in my last letter.6 I have since found myself a flowering plant, which has continued flowering in my garden for about six weeks. The flowering stem of my plant is about four (or five) years old, and four feet high, with large Veratrum-like leaves;7 it bears its golden flowers in loose compound ears in the axillæ of the leaves of the preceding year. The pollinium consists of a large boat-shaped disk, from the back of which springs a straight long staff, lying in the furrow of the anterior side of the anther.8
[2 DIAGS HERE]
(What, in the dry bud, I erroneously took for a caudiculus,9 was the tip of this staff, wrinkled and curved). When the anther opens, the numerous small pollenmasses adhere to the staff by means of elastic threads. I had no very young buds, but as far as I have seen, the staff never adheres to the dorsal surface of the rostellum, but is always free, growing downwards from the tip of the rostellum. In a bud, 6mm. long, the staff had a length of 2,5mm. and a smooth surface; in a bud 16mm long it was 4mm long and the cells near its tip had grown out into short blunt warts or hairs, probably facilitating the adhesion of the pollen masses.— This seems to me to be a fine instance of the same end being gained through different means; here, as well as in Bonatea and in many Vandeæ, the pollen-masses are borne by a long stalk; but here this stalk is a long process, freely springing from the back of the disk, whilst in Bonatea it is a metamorphosed part of the pollen-masses and in the Vandeæ a part of the dorsal wall of the rostellum.
To the list of Orchids in which own pollen decays and 〈becomes dark brown〉10 a few days after being placed on the stigma, 〈I can now add two〉 more species, viz. a second Gomeza (crispa) 〈and one〉 common Burlingtonia (decora Lem.?).—11 〈In Oncidium crispum〉 there seems to be, in this respect, a large amount 〈of ind〉ividual variability.12 On a vigorous large plant I crossed 8 flowers, all of which are producing fine pods; 12 flowers were self-fertilized, of which 7 being dissected within 10 days after fertilization showed fresh pollen and pollen-tubes; 2 dissected a fortnight after fertilization had the pollen-tubes brown and withering; 3 are producing seed capsules; of these 2 (pollen from distinct flowers of the same plant) are equal in size to the crossed pods, 1 (pollen of the same flower) is a little smaller.— On a second vigorous plant with a very large panicle I crossed 10 flowers; all have now fine pods.— 9 flowers were self-fertilized, of which 3 had fresh pollen, when dissected 6, 7, 9 days afterwards; the germens of the rest began to discolour after 9, 10, 12, 13, 14, 15 days, and showed brown pollen, when dissected.— On a third, small but healthy, plant one flower was fertilised with the same plants pollen and is yielding a pod much smaller, than that of a second crossed flower; on the stigmas of two flowers I placed one own pollen-mass and one from a distinct plant; they are producing seed-capsules equal in size to the crossed one. Lastly, on two other weak plants 3 flowers were self-fertilized and perished, the germens discolouring after 9 days.
Some Orchids, which I had supposed to be self-fertile, because self-fertilized flowers yielded fine pods, seem notwithstanding to be perfectly sterile, or nearly so, with own pollen. I examined microscopically numerous seeds taken from 19 self-fertilized pods of Epidendrum Zebra (variegatum?)13 and only in one of these pods I met with a small number of seeds having an embryo, which seemed to me unusually small;—all the rest contained only empty embryoless hides instead of seeds. This was also the case with two self-fertilized capsules of a Maxillaria. (Subgen. Xylobium).—14
Some of the pods which I had obtained by crossing distinct species of Orchids have also proved to contain only bad seeds or no seed at all; so those of Epid. Zebra (♀) crossed with Ep. fragrans and. Ep. cinnabarinum, and those of Oncidium flexuosum (♀), crossed with Cyrtopodium.15 This latter pod grew very well in the beginning, even more rapidly, than most other pods of the same plant; fertilized Jan. 17, it measured 30mm Febr. 28, whilst a pod fertilized at the same time with Oncid. pubes(?), had only 23mm. But all the seeds of the latter were apparently good. In the seedless pod of Onc. flexuosum fertilized with pollen of Cyrtopodium the hygroscopical hairs on the inside of the valves, so common among Orchids, are unusually well developed.16
How wonderful the fact is, which you observed, of the difference of growth in the plants produced from self-fertilized and crossed seeds,17 and what a fine gradation we now already have in the results of self-fertilization, from the less vigorous growth of the seedlings, through lessened number or total want of good seeds, to the mutual poisonous action of the same plants pollen and stigma.
I have lately begun collecting our Ferns and in a few weeks brought together about 50 species, belonging to more than 30 genera. It is a curious fact that even till the present day the first leaves (I do not know the proper English term for the “frondes”18 of ferns) of many exhibit the form of Cyclopteris, the dominant genus in the eldest fossil fern-flora.— I enclose here two small pretty species closely ressembling each other, though belonging to distinct genera;19 one of them, with anastomosing nerves (Doryopteris) is a most common species; the other, with free nerves (Pellæa?) seems to be very rare and I have always found it in company of Doryopteris.20 The leaves of Pellæa are generally more divided, but I have often been unable to say to which of the two species a plant belonged without looking for the nerves.— A Campyloneuron 21 growing almost always in company of a very common Drynaria also ressembles to this latter so closely, that sterile plants can often hardly be distinguished without examining their nervation. I already mentioned, I think, a small Oncidium from Theresopolis, growing in company of, and, by its pseudobulbs and leaves, closely ressembling to, Oncid. unicorne, to which it has no close systematic affinity.—22 Many years ago, on a voyage to the Itajahy, I was struck by a Papilionaceous plant, which at first sight, deceived by the colour of its leaves and flowers, I had mistaken for a common littoral Ipomoea, among which it flourished.
In most of these cases of two species of distinct genera or families growing in company of and closely ressembling, each other in colour, or odour, or form,—it will be very difficult to decide, whether this ressemblance is due to adaptation to the same conditions of life or to mimicry. In the case of the Leguminosa it seems to me by far more probable, that it is a mimetic plant.
I am quite unable to explain the fact of Echites catching insects.23 I have lately planted in my garden several species of the genus, (which, besides, are very beautiful plants) in order to have an opportunity of learning something about this fact— Your Cordia is a small shrub, and very small plants are able to flower, so that perhaps you may see your plants flowering next year.24
On the Itajahy I intend to make some essays on the domestication of some of our wild mammals (Aguti, Paca, Tapir) and birds, and one of my main occupations will be cultivating plants; so, far from not caring much, as you fear, about your new book, I look for it with an intense interest.25
I had thought of publishing a little book containing miscellaneous zoological observations, a year or more ago; but on communicating the plan to a friend of mine I knew that it would be difficult to find a publisher for such a book in Germany.26 So I have given up the idea.—
Are not climbing Genera generally more widely spread, than other genera of their family, as is for instance, the case with Clematis, or Smilax?—
Hoping that this letter will find you in good health, believe me, dear Sir, | very truly and respectfully yours | Fritz Müller
Discusses dimorphism in plants, especially the Rubiaceae.
Gives observations on orchids; notes varying degrees of self-sterility and a varying success at crossing distinct species.
Mentions local ferns he is collecting
and considers the phenomenon of apparently mimetic plants.
Please cite as
Darwin Correspondence Project, “Letter no. 5559,” accessed on 29 May 2016, http://www.darwinproject.ac.uk/DCP-LETT-5559