Anent the large nuts in the photograph, which weigh about an ounce apiece or about 28 g. (compare figures in table I), Mr. Ferguson, Instructor at the Long Island Agricultural and Technical Institute, through whom we received the nuts, states that "the nuts of the seedlings from the tree do not average better than half the size of those of the parent tree." This illustrates the fact, now well known, that the chestnut tree is self sterile. Nuts are always (with exceptions) a result of fertilization of the flowers with the pollen from another tree.
We should like to reproduce this tree in our plantations, but the only way it can be done is by grafting scions of it on to some other, preferably Japanese, stock, or by rooting cuttings from it—a method which we still have not been able to accomplish readily.
Moll-Seg, or Chinese Prolific
In the report of the senior writer for 1934 (Brooklyn Botanic Garden Record 24:62) it was stated: "In our form of the Chinese chestnut only one, if any, bur appears at the base of the flowering branch. The dwarf species, C. seguini, from eastern and central China, on the other hand, is most prolific; and in addition, blooms from June to October. It will be seen that crosses of these two species may produce valuable breeding stock." As a result of this cross, made in 1934, we obtained seven nuts, and from these nuts we have today, nineteen years later, four trees, three of which have shown marked blight resistance. One of these three is much larger, partaking more in its stature and form of the character of its Chinese parent, and in contrast to the latter, bears burs and nuts in profusion, usually clustered at the ends of the branches. (Fig. 2). The nuts are small but of good flavor. It is a good nut tree, not suitable for timber. However, as we stated in our 1951-2 report, it is subject to considerable twig blight, caused by the attacks of the weak parasite, Cryptodiaporthe castanea (Tul.) Wehmeyer, and this is due apparently to the influence of its tender parent, the Seguin chestnut, which habitually dies back in the winter. The parasite easily enters the dying ends of the twigs. We should like to see this tree tried out in a warmer climate—Georgia, Florida, Alabama, etc. Possibly it might prove adaptable to a southern European environment.[5]
[5] Systematic descriptions of this and other valuable chestnut hybrids are being prepared for publication.
Pollen Receptivity of Female Flowers
Chestnut is monecious. The flowers are borne on the present year's growth in long catkins. These are of two distinct types; near the base of the flowering branch they consist of male flowers only. The catkins near the apex, on the other hand, are bisexual; pistillate flowers are found, solitary or in clusters of two or three, near the base of this type of catkin. The remainder of the catkin bears male flowers similar to those on the all-male catkins.
The unisexual male catkins are the first to start flowering and not until two to three weeks later will the male flowers of the bisexual catkins be in full bloom. Normally, the pistillate flowers will reach full development sometime between these two periods of pollen shedding.
The Length of the Receptivity Period.—During the summer of 1953 an experiment was conducted to determine more definitely when the pistils became receptive and how long they remain in this condition. Two Chinese, two Japanese and two hybrid chestnuts of the combination (Jap. x C. pumila) x Jap., the so-called S8xJ, were used as the females in the study. Emasculation and bagging was done at the beginning of anthesis, that is, when the first unisexual male catkins began to shed pollen. Three different pollen sources were used on each female parent; they were of the same species or hybrid combination as the female. The following diagram shows the pollination schedule used.
Pollen source Time of pollination in days No. after beginning of anthesis 5 9 13 17 22 ———————————————————————- 1 X X X 2 X X X 3 X X X