The Horticulturist, 23(267): 271-272 (September, 1868)
Relation and Effects of Pollen in Cross Fertilization
Dr. Hildebrand, of Bonn, has lately been conducting some experiments with maize plants and making observations on the apple, to prove the direct influence exercised by foreign pollen on the properties of the fruit thereby produced. In Darwin's recently published work are a series of observations which go to prove that in fertilizing a plant with the pollen of a closely related species or variety, this foreign pollen not only acts on the offspring thereby generated, but may also exercise a direct influence on the shape of the seed vessel and seed of the flower operated upon—a fact previously ascertained by Wiegmann and others, which has, however, been abundantly attacked and criticised of late by Naegeli and others, and rejected as erroneous, but, it may be assumed, without good ground to the contrary.
Among the observations quoted by Darwin the following passages occur: "As long ago as the year 1751 (Philosophical Transactions, 1751, p. 206), it was observed that when different colored varieties of maize grew near together, their seeds were mutually affected, and this is now very generally accepted in the United States as an established fact. Dr. Savi (Gallesio, Teoria della Riproduzione, 1816, p. 95) carefully repeated the experiment. He sowed yellow and black seeded maize together, and in one and the same cob some of the seeds were yellow, some black, and others speckled, the different colored being either arranged in different rows or irregularly scattered."
Without knowing anything of this observation, Dr. Hildebrand experimented with varieties of maize last summer, one with yellow and the other with dark brown grain, and as this trial was most scrupulously carried out, and led to a decisive result, a description of it does not appear superfluous. In the experiments cited by Darwin, we find no guarantee that the plants employed were not raised from seeds which originated in a cross of two different varieties, so that the possibility of the seeds having become parti-colored, independently of the influence of foreign pollen, is not excluded.
Foreseeing this probable objection to the value of his experiment, Dr. Hildebrand fertilized some of the flowers of a plant, raised from yellow seed, with its own pollen, and thus saved cobs whose seeds were exactly like those sown. There can be no doubt, therefore, that there was here a pure yellow variety of maize, and not a cross derived from two different varieties. Dr. Hildebrand then raised plants of the pure yellow variety, and fertilized the female ears with pollen taken from a plant of the dark brown variety, similarly raised. The consequence was that two cobs were obtained in which about half the seeds resembled that of the mother plant, or which were perhaps a little lighter in color, while the other half were of a dirty violet color, and scattered about indiscriminately among the others, showing that the pollen from the brown variety had exercised a direct influence. In a third cob, obtained through the same process, all the seeds were pure yellow, but on one side of the axis, between two rows of seed, there was a reddish brown stripe, so that in this case it had even asserted its power in altering the color of the axis of the fruit.
All the female heads thus experimented upon were closely enveloped in paper capsules, and only partially opened to introduce the pollen, and immediately closed after each of the numerous applications, so as to avoid all possibility of any grains that might be floating about in the air coming in contact with them. Some other varieties of maize were also tried, but without success in effecting a union. Pollen from the yellow variety failed to impregnate the brown variety, although the same plant set several cobs fertilized with pollen from the same variety.
Darwin alludes to the same phenomenon as observed in the different varieties of apples, to which Dr. Hildebrand adds the following observation: "The year before last he noticed an apple on a branch of the Autumn Calville that stuck out among the branches of a neighboring Red Calville, the color of which for the greater part was the same as the remaining apples of the Autumn Calville, namely, yellow, with small red spots; but on one side, from the border of the calyx down to the stalk, there was a broad red band, just like the color of the Red Calville. Besides this outward resemblance there was also a number of red vascular bundles in the flesh beneath, which is quite characteristic of the Red Calville, so that this part resembled the latter apple in all particulars. This seems to be a case in which the pollen of one variety acted upon the other, for there is no record of any other apples of the Autumn Calville variety with red stripes."
For several years in succession Dr. Hildebrand has remarked a similar occurrence on a tree of the Strawberry Apple that was overgrown by a tree of the Red Stettiner, which he is inclined to believe was effected in the same way. In the face of the foregoing observations, and those collected by Darwin, it can scarcely be further contended that foreign pollen does not possess the power of effecting a change in the nature of the fruit resulting from its application, although it is probable that such influence is rarely exercised, or only between very closely related species or varieties. Nevertheless, so few trustworthy observations are on record that it is extremely desirable the question should be investigated further, as every additional proof might serve to convert some of the numerous unbelievers.—Gardener's Chronicle.