Muller as 100 to 61; and his are probably the more accurate of the two. The contents of the larger pollen-grains appear more coarsely granular and of a browner tint, than those in the smaller grains. The two forms of Hottonia thus agree closely in most respects with those of the heterostyled species of Primula. The flowers of Hottonia are cross-fertilised, according to Muller, chiefly by Diptera.

Mr. Scott made a few trials on a short-styled plant, and found that the legitimate unions were in all ways more fertile than the illegitimate (1/17. 'Journal of the Linnean Society Botany' volume 8 1864 page 79.); but since the publication of his paper H. Muller has made much fuller experiments, and I give his results in Table 1.13, drawn up in accordance with my usual plan:--

TABLE 1.13. Hottonia palustris (from H. Muller).

Column 1: Nature of the Union. Column 2: Number of Capsules examined. Column 3: Average Number of Seeds per Capsule.

Long-styled by pollen of short-styled. Legitimate union: 34 : 91.4.

Long-styled by own-form pollen, from a distinct plant. Illegitimate union: 18 : 77.5.

Short-styled by pollen of long-styled. Legitimate union: 30 : 66.2.

Short-styled by own-form pollen, from a distinct plant. Illegitimate union: 19 : 18.7.


The two legitimate unions together: 64 : 78.8.

The two illegitimate unions together: 37 : 48.1.

The most remarkable point in this table is the small average number of seeds from the short-styled flowers when illegitimately fertilised, and the unusually large average number of seeds yielded by the illegitimately fertilised long- styled flowers, relatively in both cases to the product of the legitimately fertilised flowers. (1/18. H. Muller says 'Die Befruchtung' etc. page 352, that the long-styled flowers, when illegitimately fertilised, yield as many seeds as when legitimately fertilised; but by adding up the number of seeds from all the capsules produced by the two methods of fertilisation, as given by him, I arrive at the results shown in Table 1.13. The average number in the long-styled capsules, when legitimately fertilised, is 91.4, and when illegitimately fertilised, 77.5; or as 100 to 85. H. Muller agrees with me that this is the proper manner of viewing the case.) The two legitimate unions compared with the two illegitimate together yield seeds in the ratio of 100 to 61.

H. Muller also tried the effects of illegitimately fertilising the long-styled and short-styled flowers with their own pollen, instead of with that from another plant of the same form; and the results are very striking. For the capsules from the long-styled flowers thus treated contained, on an average, only 15.7 seeds instead of 77.5; and those from the short-styled 6.5, instead of 18.7 seeds per capsule. The number 6.5 agrees closely with Mr. Scott's result from the same form similarly fertilised.

From some observations by Dr. Torrey, Hottonia inflata, an inhabitant of the United States, does not appear to be heterostyled, but is remarkable from producing cleistogamic flowers, as will be seen in the last chapter of this volume.

Besides the genera Primula and Hottonia, Androsace (vel Gregoria, vel Aretia) vitalliana is heterostyled. Mr. Scott fertilised with their own pollen 21 flowers on three short-styled plants in the Edinburgh Botanic Gardens, and not one yielded a single seed; but eight of them which were fertilised with pollen from one of the other plants of the same form, set two empty capsules. (1/19. See also Treviranus in 'Botanische Zeitung' 1863 page 6 on this plant being dimorphic.) He was able to examine only dried specimens of the long-styled forms. But the evidence seems sufficient to leave hardly a doubt that Androsace is heterostyled. Fritz Muller sent me from South Brazil dried flowers of a Statice which he believed to be heterostyled. In the one form the pistil was considerably longer and the stamens slightly shorter than the corresponding organs in the other form. But as in the shorter-styled form the stigmas reached up to the anthers of the same flower, and as I could not detect in the dried specimens of the two forms any difference in their stigmas, or in the size of their pollen-grains, I dare not rank this plant as heterostyled.

Charles Darwin

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