This fact agrees better with the belief that the species is dioecious than that it consists of hermaphrodites and females; for if any one of the isolated plants had been an hermaphrodite, it would probably have produced some fruit.]


This great natural family contains a much larger number of heterostyled genera than any other one, as yet known.

Mitchella repens.

Professor Asa Gray sent me several living plants collected when out of flower, and nearly half of these proved long-styled, and the other half short-styled. The white flowers, which are fragrant and which secrete plenty of nectar, always grow in pairs with their ovaries united, so that the two together produce "a berry-like double drupe." (3/22. A. Gray 'Manual of the Botany of the United States' 1856 page 172.) In my first series of experiments (1864) I did not suppose that this curious arrangement of the flowers would have any influence on their fertility; and in several instances only one of the two flowers in a pair was fertilised; and a large proportion or all of these failed to produce berries. In the ensuing year both flowers of each pair were invariably fertilised in the same manner; and the latter experiments alone serve to show the proportion of flowers which yield berries, when legitimately and illegitimately fertilised; but for calculating the average number of seeds per berry I have used those produced during both seasons.

In the long-styled flowers the stigma projects just above the bearded throat of the corolla, and the anthers are seated some way down the tube. In the short- styled flowers those organs occupy reversed positions. In this latter form the fresh pollen-grains are a little larger and more opaque than those of the long- styled form. The results of my experiments are given in Table 3.21.

TABLE 3.21. Mitchella repens.

Column 1: Nature of the Union. Column 2: Number of Pairs of Flowers fertilised during the second season. Column 3: Number of Drupes produced during the second season. Column 4: Average Number of good Seeds per Drupe in all the Drupes during the two Seasons.

Long-styled by pollen of short-styled. Legitimate union : 9 : 8 : 4.6.

Long-styled by own-form pollen. Illegitimate union : 8 : 3 : 2.2.

Short-styled by pollen of long-styled. Legitimate union: 8 : 7 : 4.1.

Short-styled by own-form pollen. Illegitimate union : 9 : 0 : 2.0.

The two legitimate unions together : 17 : 15 : 4.4.

The two illegitimate unions together : 17 : 3 : 2.1.

It follows from this table that 88 per cent of the paired flowers of both forms, when legitimately fertilised, yielded double berries, nineteen of which contained on an average 4.4 seeds, with a maximum in one of 8 seeds. Of the illegitimately fertilised paired flowers only 18 per cent yielded berries, six of which contained on an average only 2.1 seeds, with a maximum in one of 4 seeds. Thus the two legitimate unions are more fertile than the two illegitimate, according to the proportion of flowers which yielded berries, in the ratio of 100 to 20; and according to the average number of contained seeds as 100 to 47.

Three long-styled and three short-styled plants were protected under separate nets, and they produced altogether only 8 berries, containing on an average only 1.5 seed. Some additional berries were produced which contained no seeds. The plants thus treated were therefore excessively sterile, and their slight degree of fertility may be attributed in part to the action of the many individuals of Thrips which haunted the flowers. Mr. J. Scott informs me that a single plant (probably a long-styled one), growing in the Botanic Gardens at Edinburgh, which no doubt was freely visited by insects, produced plenty of berries, but how many of them contained seeds was not observed.

Borreria, nov. sp. near valerianoides (Rubiaceae).

Fritz Muller sent me seeds of this plant, which is extremely abundant in St. Catharina, in South Brazil; and ten plants were raised, consisting of five long- style

The Different Forms of Flowers on Plants of the Same Species Page 56

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Charles Darwin

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