The several foregoing facts led me to try the effects of the two kinds of pollen on the stigmas of the two forms. Four essentially different unions are possible; namely, the fertilisation of the stigma of the long-styled form by its own-form pollen, and by that of the short-styled; and the stigma of the short-styled form by its own-form pollen, and by that of the long-styled. The fertilisation of either form with pollen from the other form may be conveniently called a LEGITIMATE UNION, from reasons hereafter to be made clear; and that of either form with its own-form pollen an ILLEGITIMATE UNION. I formerly applied the term “heteromorphic” to the legitimate unions, and “homomorphic” to the illegitimate unions; but after discovering the existence of trimorphic plants, in which many more unions are possible, these two terms ceased to be applicable. The illegitimate unions of both forms might have been tried in three ways; for a flower of either form may be fertilised with pollen from the same flower, or with that from a another flower on the same plant, or with that from a distinct plant of the same form. But to make my experiments perfectly fair, and to avoid any evil result from self-fertilisation or too close interbreeding, I have invariably employed pollen from a distinct plant of the same form for the illegitimate unions of all the species; and therefore it may be observed that I have used the term “own-form pollen” in speaking of such unions. The several plants in all my experiments were treated in exactly the same manner, and were carefully protected by fine nets from the access of insects, excepting Thrips, which it is impossible to exclude. I performed all the manipulations myself, and weighed the seeds in a chemical balance; but during many subsequent trials I followed the more accurate plan of counting the seeds. Some of the capsules contained no seeds, or only two or three, and these are excluded in the column headed “good capsules” in several of the following tables:-- TABLE 1.6. Primula veris. Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. Column 3: Number of Capsules produced. Column 4: Number of good Capsules. Column 5: Weight of Seed in grains. Column 6: Calculated Weight of Seed from 100 good Capsules. Long-styled by pollen of short-styled. Legitimate union : 22 : 15 : 14 : 8.8 : 62. Long-styled by own-form pollen. Illegitimate union : 20 : 8 : 5 : 2.1 : 42. Short-styled by pollen of long-styled. Legitimate union : 13 : 12 : 11 : 4.9 : 44. Short-styled by own-form pollen. Illegitimate union : 15 : 8 : 6 : 1.8 : 30. SUMMARY: The two legitimate unions : 35 : 27 : 25 : 13.7 : 54. The two illegitimate unions : 35 : 16 : 11 : 3.9 : 35.