The great difference in the degree of sterility between the various heterostyled species when illegitimately fertilised, and between the two forms of the same species when similarly fertilised, harmonises well with the view that the result is an incidental one which follows from changes gradually effected in their reproductive systems, in order that the sexual elements of the distinct forms should act perfectly on one another.
TRANSMISSION OF THE TWO FORMS BY HETEROSTYLED PLANTS.
The transmission of the two forms by heterostyled plants, with respect to which many facts were given in the last chapter, may perhaps be found hereafter to throw some light on their manner of development. Hildebrand observed that seedlings from the long-styled form of Primula Sinensis when fertilised with pollen from the same form were mostly long-styled, and many analogous cases have since been observed by me. All the known cases are given in Tables 6.36 and 6.37.
TABLE 6.36. Nature of the offspring from illegitimately fertilised dimorphic plants.
Column 1: Species and form. Column 2: Number of long-styled offspring. Column 3: Number of short-styled offspring.
Primula veris. Long-styled form, fertilised by own-form pollen during five successive generations : 156 : 6.
Primula veris. Short-styled form, fertilised by own-form pollen : 5 : 9.
Primula vulgaris. Long-styled form, fertilised by own-form pollen during two successive generations : 69 : 0.
Primula auricula. Short-styled form, fertilised by own-form pollen, is said to produce during successive generations offspring in about the following proportions : 25 : 75.
Primula Sinensis. Long-styled form, fertilised by own-form pollen during two successive generations : 52 : 0.
Primula Sinensis. Long-styled form, fertilised by own-form pollen (Hildebrand) : 14 : 3.
Primula Sinensis. Short-styled form, fertilised by own-form pollen: 1 : 24.
Pulmonaria officinalis. Long-styled form, fertilised by own-form pollen : 11 : 0.
Polygonum fagopyrum. Long-styled form, fertilised by own-form pollen : 45 : 4.
Polygonum fagopyrum. Short-styled form, fertilised by own-form pollen : 13 : 20.
TABLE 6.37. Nature of the offspring from illegitimately fertilised trimorphic plants.
Column 1: Species and form. Column 2: Number of long-styled offspring. Column 3: Number of mid-styled offspring. Column 4: Number of short-styled offspring.
Lythrum salicaria. Long-styled form, fertilised by own-form pollen : 56 : 0 : 0.
Lythrum salicaria. Short-styled form, fertilised by own-form pollen : 1 : 0 : 8.
Lythrum salicaria. Short-styled form, fertilised by pollen from mid-length stamens of long-styled form : 4 : 0 : 8.
Lythrum salicaria. Mid-styled form, fertilised by own-form pollen : 1 : 3 : 0.
Lythrum salicaria. Mid-styled form, fertilised by pollen from shortest stamens of long-styled form : 17 : 8 : 0.
Lythrum salicaria. Mid-styled form, fertilised by pollen from longest stamens of short-styled form : 14 : 8 : 18.
Oxalis rosea. Long-styled form, fertilised during several generations by own- form pollen, produced offspring in the ratio of : 100 : 0 : 0.
Oxalis hedysaroides. Mid-styled form, fertilised by own-form pollen : 0 : 17 : 0.
We see in these two tables that the offspring from a form illegitimately fertilised with pollen from another plant of the same form belong, with a few exceptions, to the same form as their parents. For instance, out of 162 seedlings from long-styled plants of Primula veris fertilised during five generations in this manner, 156 were long-styled and only 6 short-styled. Of 69 seedlings from P. vulgaris similarly raised all were long-styled. So it was with 56 seedlings from the long-styled form of the trimorphic Lythrum salicaria, and with numerous seedlings from the long-styled form of Oxalis rosea. The offspring from the short-styled forms of dimorphic plants, and from both the mid-styled and short-styled forms of trimorphic plants, fertilised with their own-form pollen, likewise tend to belong to the same form as their parents, but not in so marked a manner as in the case of the long-styled form.