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Letter 5429

Müller, J. F. T. to Darwin, C. R.

4 Mar 1867

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    Reports observations on fertility of orchids he has self-pollinated and crossed with pollen of other species.

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Desterro, Brazil, March 4. 1867. My dear Sir

I am very much obliged to you and thank you cordially for Bentham's and Hooker's Genera Plantarum, which I received in due time and which have already been very serviceable to me. The ``conspectus generum'' and the list of the abnormal and allied forms at the head of each order facilitate extraordinarily the task of finding the name of any unknown genus. I was surprised at seeing that the authors never had an opportunity of examining the seeds of some of our most common and conspicuous plants, such as Schizolobium and Norantea. I should be very glad, if I could satisfy any wish, which the authors might have respecting to our flora.

I have also to thank you for your kind letter of Jan. 1st, and will now first answer the questions, you ask in this letter. As to Adenanthera pavonina, the only tree, I know, stands in a garden; but I had not even suspected, that it had been planted there, and still less, (as we are here very rich in Mimoseæ) that the species had been introduced from India.— The Oncidium flexuosum is an endemic species and is even the most common species of that genus.— There is now flowering another common species of Oncidium, perhaps the O. micropogon Rchb. f. in which pollen and stigma of the same individual plant have the same deletery action on each other, which they have in O. flexuosum, unicorne and pubes(?).— This is also the case with a species of Gomeza R. Br. (Rodriguezia Lindl.), and with a small, but extremely pretty Sigmatostalix Rchb. f. (S. tricolor n. sp?). The same plants of Gomeza and of the several species of Oncidium on which I ascertained this fact, were fertile with pollen of other plants of the species. Of Sigmatostalix I have but one flowering plant.

[dried specimen] Flower of Gomeza, split longitudinally 3 days after fertilization with own pollen.

Another allied Orchid, which is even placed in the same genus (Odontoglossum) with Gomeza by Mr. Reichenbach, the Aspasia lunata, is fertile with own pollen; I had a single flower, which being fertilised with its own pollen, is yielding a seed-capsule.

I have now had several ears of the Notylia (pubescens?) of which I could not fertilize the few flowers, I observed last year. The stigmatic slit, extremely narrow, when the flower expands, widens gradually in the course of the next days and 2 or 3 days afterwards fertilization is effected rather easily. Even during the first day I sometimes succeeded in introducing dry pollenmasses. The stigma has room only for one pollen mass, as is also the case with Ornithocephalus so that in Notylia each pollinium may fertilize two and in Ornithocephalus four flowers. (In some Vandeæ with 4 pollen masses the anterior pair covers the posterior so completely, that the latter can touch the stigma only after the removing of the former; and thus each pollinium is apt to fertilize two flowers; so it is, for instance, with Dichæa and with the most beautiful of all our Vandeæ, the Zygopetalum maxillare).— As in our other Notylia, the same individual plants pollen soon becomes blackish-brown in the stigmatic chamber, whilst pollen of any other plant of the species remains fresh, emits tubes ec.—

[DIAG HERE]

Pollinia of a Dichæa (with dark-blue lip) a. anterior pollenmasses, concealing the smaller posterior ones. b. posterior pollen masses, after fertilizing a flower with the anterior ones. c caudicles of the removed anterior pollen masses.

All the Epidendreæ, I hitherto tried, are fertile with own pollen; but from some experiments on Epidendrum cinnabarinum I suspect, that they will be less fertile with own, than with a distinct plants pollen. From several flowers, fertilized (Decbr. 20) with their own pollen, I obtained two pods, (ripe Febr. 19 & 20), the seeds of each of which weighed 5 grains. An ear of a second plant, the flow<ers> <of which were> fertilized (Decbr. 20) with pollen of a <    > same plant yielded two pods also <    > seeds weighing 5.5 and 6 grains.

A second ear of the same plant <was fertilized with> pollen of a distinct plant of the species (Decbr. <    >) <    > pod (ripe febr. 17), the seeds of which weighed 12,5 grains—more than those of both the pods fertilised with pollen of the same plant.

Three capsules of a third plant, fertilised (Decbr. 21) with pollen of a distinct plant, (ripe febr. 17), contained 26 grains of seeds; (each capsule, on an average, 8.7 grains).—

Lastly—and this is rather curious, a pod of a fourth plant, fertilised (Decbr. 21) with pollen of a distinct species (Ep. Schomburgkii?), (ripe febr. 17), was larger than all the other pods and its seeds weighed 14 grains! A second pod of Ep. cinnabarinum fertilized (Jan. 18) with pollen of Ep. Schomburgkii, is also much larger, than several pods, fertilized (febr. 17) with pollen of the own species.

Among 300 seeds from a pod fertilised with the same plants pollen only 86 seemed to be good, while at least 9/10 appeared to be so in the pods fertilised by pollen of a distinct plant of the species or of Ep. Schomburgkii.

Fertilisation with own pollen, at least in Orchids, seems to have much analogy with illegitimate unions of dimorphic plants or crossing of distinct species. it might be interesting to compare the offspring of plants fertilised with own pollen with hybrids and the illegitimate offspring of dimorphic plants. May not the individual plants of some species, which were found to be quite sterile with own pollen, have been the offspring of flowers fertilized with own pollen?

<dried specimen excised> I enclose a dimorphic Rubiaceæ, probably a Diodia. (I have not yet examined ripe fruits, which furnish the main distinction between this genus, Borreria and Spermacoce) There is a small, but as far, as I have seen, constant, difference in the size of the pollen-grains, those of the short-styled flowers being larger.

I had promised you to try some experiments on the fertilisation of Scaevola; but all the plants, which at several occasions I have brought home, have perished and from all the seeds, I planted, I did not obtain a single plant. In some other cases I have also utterly failed in transplanting into my garden plants growing in the loose sand of the sea-shore.—

The copies of the paper on climbing plants, which you have been so good as to send me, have not yet arrived.

Permit me again to thank you cordially for your great kindness and Believe me, dear Sir, | very sincerely and respectfully yours | Fritz Müller.

    Footnotes Add

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    f1 5429.f1
    In his letter of 23 August [1866] (Correspondence vol. 14), CD had offered to send Müller a copy of the first two parts of Genera plantarum by George Bentham and Joseph Dalton Hooker (Bentham and Hooker 1862--83), which was published in seven parts. The first part appeared in 1862, the second in 1865. CD reported sending the volumes in his letter of [late December 1866 and] 1 January 1867 (Correspondence vol. 14).
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    f2 5429.f2
    `Conspectus generum': overview of genera (Latin).
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    f3 5429.f3
    For the descriptions of Norantea and Schizolobium, see Bentham and Hooker 1862--83, 1: 181, 569.
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    f4 5429.f4
    See Correspondence vol. 14, letter to Fritz Müller, [late December 1866 and] 1 January 1867.
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    f5 5429.f5
    Müller had sent CD seeds which he described as coming from `a tree, probably belonging to the Mimoseae' (Correspondence vol. 14, letter from Fritz Müller, 1 and 3 October 1866). CD sent some of the seeds to Hooker, who identified them as seeds of Adenanthera pavonina, a tree native to India (see Correspondence vol. 14, letter to Fritz Müller, [late December 1866 and] 1 January 1867 and n. 14).
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    f6 5429.f6
    In his letter of [late December 1866 and] 1 January 1867 (Correspondence vol. 14), CD had asked whether Oncidium flexuosum was endemic to Brazil. CD later asked whether the species was native to the area where Müller lived, noting that he had previously attributed similar cases of self-sterility to cultivation under unnatural conditions (see letter to Fritz Müller, 7 February [1867] and n. 6).
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    f7 5429.f7
    Müller never published the name Sigmatostalix tricolor; however, the species he refers to is probably S. radicans (a synonym of Ornithophora radicans), which is native to Santa Catarina (Pabst and Dungs 1975--7, 2: 199).
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    f8 5429.f8
    Müller attached a number of plant specimens to this letter; none of the other surviving specimens is labelled.
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    f9 5429.f9
    Müller refers to Heinrich Gustav Reichenbach. Gomeza is now Gomesa.
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    f10 5429.f10
    Müller first described the case of Notylia in his letter of 2 August 1866 (Correspondence vol. 14); he had initially supposed that the plant was male because he could not get pollinia to adhere to the stigma and the ovules seemed rudimentary, but later found seed capsules and hypothesised that the ovules matured some time after the flower opened. See also Correspondence vol. 14, letter to Fritz Müller, 25 September [1866] and nn. 3--6). CD added Müller's observation on the widening of the stigmatic slit to Orchids 2d ed., p. 172.
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    f11 5429.f11
    The genera Notylia, Ornithocephalus, Dichaea, and Zygopetalum were all included within the tribe Vandeae (Lindley 1853; Endlicher 1836--42). For an updated classification of these genera, see Dressler 1993, pp. 272--3.
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    f12 5429.f12
    CD had told Müller of his plan to carry out experiments comparing the growth rates of `plants raised from seed fertilized by pollen from the same flower & by pollen from a distinct plant' (see Correspondence vol. 14, letter to Fritz Müller, 25 September [1866]). CD's earlier work on dimorphic and trimorphic plants had suggested that fertility was dependent on whether pollen from the same or different form of plant was used; he had referred to the crosses of plants of the same form as `homomorphic' unions and later as `illegitimate' (see `Dimorphic condition in Primula', p. 87 (Collected papers 2: 55), and `Three forms of Lythrum salicaria', p. 187 (Collected papers 2: 121)).
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    f13 5429.f13
    The genus Borreria is now subsumed within the genus Spermacoce (Mabberley 1997).
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    f14 5429.f14
    CD had noted differences in pollen-grain size in his experiments with dimorphic and trimorphic plants (see `Dimorphic condition in Primula', pp. 78--9 (Collected papers 2: 46), `Two forms in species of Linum', p. 75 (Collected papers 2: 98), and `Three forms of Lythrum salicaria', pp. 170--3 (Collected papers 2: 106--9)).
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    f15 5429.f15
    In a letter of 5 November 1865 (Correspondence vol. 13), Müller had mentioned a Scaevola growing on the east coast of the island of Santa Catarina, Brazil. In his letter to Fritz Müller, [9 and] 15 April [1866] (Correspondence vol. 14), CD wrote, `I have long wished some one to observe the fertilization of Scævola' and reported his own observations. No letter from Müller promising to try experiments with Scaevola has been found, but in a letter to his brother Hermann of 29 October 1866 (Möller ed. 1915--21, 2: 97--8), Müller described the pollination mechanism of the specimens he observed in the wild, confirming CD's observations (see also a similar description in F. Müller 1868a, pp. 114--15).
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    f16 5429.f16
    The reference is to Müller's paper on climbing plants, copies of which had been sent by CD (F. Müller 1865; see Correspondence vol. 14, letter to Fritz Müller, [late December 1866 and] 1 January 1867 and n. 15).
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    f17 5429.f17
    CD wrote the name `Diodæa' (sic for Diodia) on the envelope, which probably contained the now missing specimen that Müller sent. CD evidently amended the name on the envelope after receiving Müller's letter of 2 June 1867, in which the identification of the specimen was corrected.
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