Discusses dimorphism of Oxalis; one form has 99% sterile anthers. Has found three kinds of fertile anthers.
My dear Sir.
In your last letter (of May 23
Now in nine stalks the flowers showed the following combinations of the different anthers:
In the first form the anthers are always fertile; but even here, as in the fertile anthers of the second form there is among the good pollen a large amount of aborted pollen-grains.
In some rather rare specimens of the second form,—but only, as far as I know, among those with sterile anthers,—the length of the stamens is very variable; (such were casually the few plants, which I had examined, when writing my last letter). Sometimes, in a single flower the longer stamens are hardly as long, and the shorter ones half as long as the styli; but even in those specimens the stamens and styli of the majority of flowers use to show the characteristic lengths of the form.
It is not very rare to find one or two of the white pollen-less anthers transformed into small leaflets, and I met with a single plant, (now in my garden), in which all the anthers are transformed into petala-like leaves, sometimes exceeding ten in number; the ovaries form five open leaves with green stigmas on the tip, but without ovula, and in the midst of these ovarial leaves there is a great number of petala-like leaves, among which sometimes some sepala may be distinguished.
Although the plant is extremely common (thousands flourishing in the very streets of our town) I have not yet been able to find a single seed-capsule. This sterility may be owing in part to the circumstance of the two forms but seldom growing mingled. You may find your way bordered, for a mile or more, by one of the two forms exclusively, which then suddenly is substituted by the other.
A second very common species of Oxalis, with small yellow flowers, is monomorphic, the styli reaching to the level of the longer stamens; this species produces plenty of seed-capsules.
Of a third species with fine crimson flowers, ressembling in shape, size and colour those of Linum grandiflorum, I have as yet seen only one plant, in which the styli were intermediate in length between the two sets of stamens; although the stigmas of all the flowers were densely covered with pollen, I found no seed-capsules; thus I am inclined to think that it will prove dimorphic or trimorphic.
In short, I hope to have an opportunity of examining a fourth species of Oxalis with woody stem.—
To the list of dimorphic plants I may add a Cordia, of which I enclose a short- styled as well as a long-styled specimen; as soon as they are ripe, I shall send you seeds of either form.—
In my last letter (of Aug. 2
Octbr. 3. Yesterday I procured to calculate the number of seeds
contained in a large capsule of an Orchid (Maxillaria?); the seeds weighed 42
Hoping that this will find you in good health I am dear Sir with the most sincere respect | Yours very truly | Fritz Müller
Do the aërial roots of all the species of Catasetum grow perpendicularly upwards into the air, as they do in our Cat. mentosum?
- f1 5226.f1See letter to Fritz Müller, 23 May 1866.
- f2 5226.f2See letter from Fritz Müller, 2 August 1866 and n. 2. After further observations, Müller later came to regard this species of Oxalis as trimorphic (see n. 6, below).
- f3 5226.f3In his work on dimorphic and trimorphic flowers, CD noted any differences in the pollen of different forms of flowers (see `Dimorphic condition in Primula', `Two forms in species of Linum', and `Three forms of Lythrum salicaria'). CD had recently been interested in the observations made by his son William Erasmus Darwin on the differences in the size of pollen-grains in Rhamnus cathartica, but was unsure of the significance of such differences. William had suggested that R. cathartica was an example of a dimorphic species becoming dioecious (see letter to W. E. Darwin, 22 June  and n. 3). CD included Müller's description of this species of Oxalis in Forms of flowers, pp. 180--1.
- f4 5226.f4Müller initially had noted considerable variation in the length of the styles, even in flowers of the same plant (see letter from Fritz Müller, 2 August 1866).
- f5 5226.f5In Forms of flowers, p. 180, CD mentioned that the stamens in some of the flowers were `partially converted into petals'.
- f6 5226.f6Müller eventually reinterpreted the cause of sterility in this species of Oxalis, as well as its dimorphic status, in light of CD's experimental results with the illegitimate offspring of various heterostyled species. He concluded that the plants might be the variable and sterile offspring of a single form of a trimorphic species, accidentally introduced and afterwards propagated asexually (see Forms of flowers, pp. 180--1; see also letter from Fritz Müller, 31 October 1868, Calendar no. 6439).
- f7 5226.f7CD discussed this monomorphic species of Oxalis in Forms of flowers, pp. 181--2.
- f8 5226.f8In Forms of flowers, p. 180, CD referred to a trimorphic Oxalis with red flowers that, according to Müller, had never produced seed.
- f9 5226.f9The specimens have not been found (see letter to Fritz Müller, [before 10 December 1866] and n. 5).
- f10 5226.f10CD cut out the following paragraph and pasted it into his Experimental notebook along with his own notes on brightly coloured seeds (DAR 157a: 80; the fragment has since been moved to DAR 157a: 103). For Müller's earlier comments on the topic, see the letter from Fritz Müller, 2 August 1866 and nn. 14 and 15.
- f11 5226.f11Müller evidently sent specimens of these seeds, but they have not been found (see letter to J. D. Hooker, 5 December  and letter to Fritz Müller, [before 10 December 1866]).
- f12 5226.f12The sketch is reproduced at approximately 80 per cent of its original size.
- f13 5226.f13Catasetum mentosum is a synonym of C. atratum.