The stamens do not differ so much in relative length as the pistils. The pollen-grains differ in a marked manner in the two forms; "those of the long-styled plants are sharply triquetrous, smaller, and more transparent than those of the short-styled, which are of a bluntly triangular form." The fertility of the two legitimate unions to that of the two illegitimate unions is by the first standard as 100 to 95, and by the second standard as 100 to 31.

Primula cortusoides.

The pistil of the long-styled form is about thrice as long as that of the short- styled, the stigma being double as long and covered with much longer papillae. The pollen-grains of the short-styled form are, as usual, "larger, less transparent, and more bluntly triangular than those from the long-styled plants." The fertility of the two legitimate unions to that of the two illegitimate unions is by the first standard as 100 to 74, and by the second standard as 100 to 66.

Primula involucrata.

The pistil of the long-styled form is about thrice as long as that of the short- styled; the stigma of the former is globular and closely beset with papillae, whilst that of the short-styled is smooth and depressed on the apex. The pollen- grains of the two forms differ in size and transparency as before, but not in shape. The fertility of the two legitimate to that of the two illegitimate unions is by the first standard as 100 to 72; and by the second standard as 100 to 47.

Primula farinosa.

According to Mr. Scott, the pistil of the long-styled form is only about twice as long as that of the short-styled. The stigmas of the two forms differ but little in shape. The pollen-grains differ in the usual manner in size, but not in form. The fertility of the two legitimate to that of the two illegitimate unions is by the first standard as 100 to 71, and by the second standard as 100 to 44.]

SUMMARY ON THE FOREGOING HETEROSTYLED SPECIES OF PRIMULA.

TABLE 1.12. Summary on the Fertility of the two Legitimate Unions, compared with that of the two Illegitimate Unions, in the genus Primula. The former taken at 100.

Column 1: Name of Species. Column 2: Illegitimate Unions, Judged of by the Proportional Number of Flowers which produced Capsules. Column 3: Illegitimate Unions, Judged of by the Average Number (or Weight in some cases) of Seeds per Capsule.

Primula veris : 69 : 65.

Primula elatior : 27 : 75 (Probably too high).

Primula vulgaris : 60 : 54 (Perhaps too low).

Primula Sinensis : 84 : 63.

Primula Sinensis (second trial) : ? : 53. Primula Sinensis (after Hildebrand) : 100 : 42.

Primula auricula (Scott) : 80 : 15.

Primula Sikkimensis (Scott): 95 : 31.

Primula cortusoides (Scott): 74 : 66.

Primula involucrata (Scott): 72 : 48.

Primula farinosa (Scott): 71 : 44.

Average of the nine species : 88.4 : 61.8.

The fertility of the long-and short-styled plants of the above species of Primula, when the two forms are fertilised legitimately, and illegitimately with pollen of the same form taken from a distinct plant, has now been given. The results are seen in Table 1.12; the fertility being judged by two standards, namely, by that of the proportional number of flowers which yielded capsules, and by that of the average number of seeds per capsule. But for full accuracy many more observations, under varied conditions, would be requisite.

With plants of all kinds some flowers generally fail to produce capsules, from various accidental causes; but this source of error has been eliminated, as far as possible, in all the previous cases, by the manner in which the calculations have been made. Supposing, for instance, that 20 flowers were fertilised legitimately and yielded 18 capsules, and that 30 flowers were fertilised illegitimately and yielded 15 capsules, we may assume that on an average an equal proportion of the flowers in both lots would fail to produce capsules from various accidental causes; and the ratio of 18/20 to 15/30, or as 100 to 56 (in whole numbers), would show the proportional number of capsules due to the two methods of fertilisation; and the number 56 would appear in the left-hand column of Table 1.12, and in my other tables.

The Different Forms of Flowers on Plants of the Same Species Page 21

19th Century English Literature

Charles Darwin

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