Pollen Quantity

Cook: Rose Hybridization (1905)
As the pollen sometimes is very scarce, it is better to put it only on two, or three pistils, repeating the operation the following day.

Cook: Some Interesting Results in Rose Hybridization (1906)
It took twenty flowers of the Marechal Niel to produce enough pollen to fertilize one flower.

14 'Beitrage zur Kenntniss,' &c., 1844, s. 345.
15 'Nouvelles Archives du Museum,' tom. i. p. 27. 1865

Variation of Animals and Plants vol. 2
Charles Darwin
With respect to plants, nearly the same results were obtained by Kölreuter and Gärtner. This last careful observer, after making successive trials on a Malva with more and more pollen-grains, found,14 that even thirty grains did not fertilise a single seed; but when forty grains were applied to the stigma, a few seeds of small size were formed. In the case of Mirabilis the pollen grains are extraordinarily large, and the ovarium contains only a single ovule; and these circumstances led Naudin15 to make the following experiments: a flower was fertilised by three grains and succeeded perfectly; twelve flowers were fertilised by two grains, and seventeen flowers by a single grain, and of these one flower alone in each lot perfected its seed: and it deserves especial notice that the plants produced by these two seeds never attained their proper dimensions, and bore flowers of remarkably small size. From these facts we clearly see that the quantity of the peculiar formative matter which is contained within the spermatozoa and pollen-grains is an all-important element in the act of fertilisation, not only for the full development of the seed, but for the vigour of the plant produced from such seed.

The Principles of Botany, and of Vegetable Physiology (1805)
Karl Ludwig Willdenow
§ 291.
Koelreuter examined, in a very laborious manner, how many globules of pollen might be required to complete an impregnation. His chief discoveries on this point are as follow:
   All the anthers of Hibiscus syriacus contained 4863 globules of pollen, 50 or 60 of which were necessary to complete impregnation. But whenever he took less than 50 globules, then not all the seeds ripened, but those, which were formed, were perfect. Ten globules were the least he could take in this flower, as less would not suffice for it. The Mirabilis Jalappa had 293 globules of pollen in one flower, Mirabilis longiflora 321. But in each of the two plants 2 or 3 globules were sufficient for impregnation. The seed did not appear more perfect, though many more globules were put upon the stigma.
   To ascertain whether, in flowers with more than one style, each ought to become impregnated separately, Koelreuter in several of them cut all off but one, and the fecundation was as successful as ever. Even in flowers, in which the style was entirely separated, fecundation took place through one of them. These experiments shew, that the hollow tubes of one style communicate with all the rest, and that more styles and more pollen are formed, merely to ensure their final determination. From this circumstance philosophers have concluded, that the cellular texture of all germens fixed in the receptacle, must cohere amongst each other.

Tomato Growers Co-operative 16: 11–12. 1966.
Pollen germination as affected by variety and number of pollen grains.
Hornby, C. A., and W. B. Charles.
During the work on developing cool-temperature tolerant tomatoes, there was reason to question the effects of amounts of pollen on a given stigma, as well as of genetic differences between varieties. Pollen grains were counted and applied to stigmas, and after 48 hours, stigmas were removed. After staining with water soluble aniline blue, the pollen tubes could be counted under ultraviolet light. Several experiments yielded similar results, and can be illustrated with the following data which is expressed as means of percentages of pollen germination from three replications.

Number of pollen
grains per stigma
Percentages pollen germination / Variety
Puck Bonny Best
15 0 0
50 11 0
100 23 14
200 37 10

There were highly significant differences between varieties and among the numbers of pollen grains used per stigma.

Some apparent genetic differences in pollen germination may be a result of "density" of pollen on a given stigma.

American Journal of Botany 86:261-268. (1999)
The effects of pollen load size and donor diversity on pollen performance, selective abortion, and progeny vigor in Mirabilis jalapa (Nyctaginaceae)
Richard A. Niesenbaum
The influence of pollen competitive environment on pollen performance (pollen germination, stigmatic penetration, and pollen tube growth rate), the maturation or abortion of initiated fruit, seed size, and seedling vigor was explored by manipulating the size and diversity of stigmatic pollen loads on Mirabilis jalapa. All aspects of pollen performance significantly increased with the number of pollen grains on a stigma or pollen tubes in a style, but was not influenced by the diversity of pollen donors. Plants tended to mature single-ovulate fruits that came from flowers where pollen load size and diversity were greatest and aborted those where these were lowest. No plants from seeds resulting from pollinations with a single pollen grain survived, but other fitness measures were mostly determined by maternal plant. The data suggest that pollen performance is influenced by pollen competitive environment, and both the genetic diversity of the pollen load and number of competing pollen tubes are important determinants of seed/fruit abortion.