In 1866 Professor Hildebrand proved by an examination of the specimens in several herbaria that 20 species are certainly heterostyled and trimorphic, and 51 others almost certainly so. (4/12. 'Monatsber. der Akad. der Wiss. Berlin' 1866 pages 352, 372. He gives drawings of the three forms at page 42 of his 'Geschlechter-Vertheilung' etc. 1867.) He also made some interesting observations on living plants belonging to one form alone; for at that time he did not possess the three forms of any living species. During the years 1864 to 1868 I occasionally experimented on Oxalis speciosa, but until now have never found time to publish the results. In 1871 Hildebrand published an admirable paper in which he shows in the case of two species of Oxalis, that the sexual relations of the three forms are nearly the same as in Lythrum salicaria. (4/13. 'Botanische Zeitung' 1871 pages 416 and 432.) I will now give an abstract of his observations, and afterwards of my own less complete ones. I may premise that in all the species seen by me, the stigmas of the five straight pistils of the long-styled form stand on a level with the anthers of the longest stamens in the two other forms. In the mid- styled form, the stigmas pass out between the filaments of the longest stamens (as in the short-styled form of Linum); and they stand rather nearer to the upper anthers than to the lower ones. In the short-styled form, the stigmas also pass out between the filaments nearly on a level with the tips of the sepals. The anthers in this latter form and in the mid-styled rise to the same height as the corresponding stigmas in the other two forms.

Oxalis Valdiviana.

This species, an inhabitant of the west coast of South America, bears yellow flowers. Hildebrand states that the stigmas of the three forms do not differ in any marked manner, but that the pistil of the short-styled form alone is destitute of hairs. The diameters of the pollen-grains are as follows:--

Table 4.b. Oxalis Valdiviana. Diameters of pollen-grains in divisions of the micrometer.

Column 1: Source of Pollen-grains. Column 2: Minimum diameter. Column 3: Maximum diameter.

From the: Longest stamens of short-styled form : 8 to 9. Mid-length stamens of short-styled form : 7 to 8. Longest stamens of mid-styled form : 8. Shortest stamens of mid-styled form : 8. Mid-length stamens of long-styled form : 7. Shortest stamens of long-styled form : 6.

Therefore the extreme difference in diameter is as 8.5 to 6, or as 100 to 71. The results of Hildebrand's experiments are given in Table 4.27, drawn up in accordance with my usual plan.

Table 4.27. Oxalis Valdiviana (from Hildebrand).

Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. Column 3: Number of Capsules produced. Column 4: Number of Seeds per Capsule.

Long-styled by pollen of longest stamens of short-styled. Legitimate union : 28 : 28 : 11.9.

Long-styled by pollen of longest stamens of mid-styled. Legitimate union : 21 : 21 : 12.0.

Long-styled by pollen of own and own-form mid-length stamens. Illegitimate union : 40 : 2 : 5.5.

Long-styled by pollen of own and own-form shortest stamens. Illegitimate union : 26 : 0 : 0.

Long-styled by pollen of shortest stamens of short-styled. Illegitimate union : 16 : 1 : 1.

Long-styled by pollen of shortest stamens of mid-styled. Illegitimate union : 9 : 0 : 0.

Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union : 38 : 38 : 11.3.

Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union : 23 : 23 : 10.4.

Mid-styled by pollen of own and own-form longest stamens. Illegitimate union : 52 : 0 : 0.

Mid-styled by pollen of own and own-form shortest stamens. Illegitimate union : 30 : 1 : 6.

Mid-styled by pollen of shortest stamens of long-styled. Illegitimate union : 16 : 0 : 0.

Mid-styled by pollen of longest stamens of short-styled. Illegitimate union : 16 : 2 : 2.5.

Short-styled by pollen of shortest stamens of long-styled. Legitimate union: 18 : 18 : 11.0.

Charles Darwin

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