Pollen from different stamens of the same flower

Journal of Horticulture and Practical Gardening, 1: 312-313 (July 23, 1861)
Donald Beaton
In the great bulk of the Scarlet or Horseshoe Geraniums there are but seven stamens, four long ones, one of medium length, but which is often wanting, and two almost sessile like the anthers of Wheat—that is, very short indeed, and opening at the bottom face to face. These two are they which reduce a whole family to beggary; first to dwarfs or Tom Thumbs, or better still, to minimums, or the smallest of that kind consistent with vigour sufficient to become a useful plant in cultivation, and, lastly, to the brink of ruin, and drive that race out of existence altogether, if there were not other means provided to arrest the decline, or keep it from manifesting itself at all in a state of Nature.

Journal of Horticulture and Cottage Gardener, 2: 41-43 (October 15, 1861)
Isaac Anderson Henry
Mr. Beaton as the first, perhaps, to find out, and certainly the first so far as I know, to announce this strange discovery, is entitled to its full merit. Its full value has not yet been sufficiently tested. For although I have produced the tiny things in the Rhododendron family which he has done with Pelargonium, inquiry should not stop here. And for my part I did not limit my aim merely to produce by them more dwarfish plants than the parents. Regarding as I did, the pollen of these small anthers as of finer particles than the pollen of the longer and larger ones, I used it as a provision of Nature's own suggesting, in preference to the latter in crossing the smaller species whose pollen-tubes I feared might not admit the grosser globules of these larger anthers. And when the two dwarf stamens failed, I used the smallest and shortest of the remaining stamens. I still cling to the belief that in this way I effected crosses in which with larger anthers I should have failed. I look on them as affording the chance of effecting unions with remote species or genera—as the links, in short, by which large and family groups might he united.

Sexual Plant Reproduction, 3(1): 7-17 (February, 1990)
Relationships of pollen size, pistil length and pollen tube growth rates in Rhododendron and their influence on hybridization.
E. G. Williams and J. L. Rouse
Pollen size and pistil length data have been collected for 93 species of Rhododendron (Ericaceae) belonging to a number of different subgeneric taxa. For a sample of eight species in section Vireya, pollen tube growth in the style after self- or interspecific pollination has been quantified. Pollen volume and the time taken for pollen tubes to reach the ovary were both related to pistil length. Pollen-tube growth rates were generally greater for species with longer pistils and larger pollen. Increasing temperature increased the rate of pollen-tube growth. There was no detectable effect of pollen tube density on tube growth rate in the style. After interspecific pollinations tube growth rates in foreign styles could be faster or slower than in self styles. A semisterile individual with two viable pollen grains per tetrad and a plant grafted as scion to a longer-styled stock both showed more rapid pollen-tube growth than expected on the basis of pistil size. Data collected for 26 species in section Vireya showed that where extreme disparity of pollen/pistil size causes failure of interspecific crosses, one or more bridging species with intermediate pollen/pistil size can generally be selected.

Effects Of Cross And Self Fertilisation In The Vegetable Kingdom
Charles Darwin
*It is, however, possible that the stamens which differ in length or construction in the same flower may produce pollen differing in nature, and in this manner a cross might be made effective between the several flowers on the same plant. Mr. Macnab states in a communication to M. Verlot 'La Production des Varietes' 1865 page 42, that seedlings raised from the shorter and longer stamens of rhododendron differ in character; but the shorter stamens apparently are becoming rudimentary, and the seedlings are dwarfs, so that the result may be simply due to a want of fertilising power in the pollen, as in the case of the dwarfed plants of Mirabilis raised by Naudin by the use of too few pollen-grains. Analogous statements have been made with respect to the stamens of Pelargonium. With some of the Melastomaceae, seedlings raised by me from flowers fertilised by pollen from the shorter stamens, certainly differed in appearance from those raised from the longer stamens, with differently coloured anthers; but here, again, there is some reason for believing that the shorter stamens are tending towards abortion.

CybeRose note: MacNab learned of this from Anderson-Henry, who worked for him at the Royal Botanic Garden of Edinburg.

Hybridizing at the Antipodes, Int'l Conf. on Genetics (1906)
H. H. B. Bradley
   Seeing that the top division of the perianth is always the largest and best coloured, I generally use the anther, the filament of which is adnate to this division; whether this be the reason or not I do not know, but the progeny generally have more equal divisions to the perianth, and the bottom division is greatly improved.
   On the other hand, with a view to getting as white a bloom as possible, I use the bottom division (generally all white) from the white red-striped varieties; and in the seedlings the flowers have much less colour; but the shape of the bloom is spoilt, the divisions being narrow.