HEREDITY IN TREES AND PLANTS
By Dr. A. F. Blakeslee, New York
Dr. Blakeslee said in part:
One of the first things we notice as we go out into the open is diversity in the habits of trees and plants. It is through the details thus presented that we are able to distinguish one species from another. You can see this diversity the year round in nut trees, and in the nuts.
If you arrange nuts, or any other objects for that matter, in a curve according to size, you will find that the most numerous of them are of about the average size. This is equally true when applied to mankind. What is the reason?
There are a number of factors affecting this, but, in general, there are two main causes—environment and heredity. We do not know which is the more important but both are absolutely necessary.
In the picture being shown we see the influence of the black walnut upon plants around it. It creates an environment which influences the ability of other plants to grow near the roots.
It must be remembered, however, that what the animate plant transmits is not the actual character in question, but the ability of the animate plant to develop characteristics. By placing the plant near a black walnut tree we do not affect anything but the capacity of the plant to develop in certain directions.
I have shown here a diagram to illustrate a certain stock fertilization. Here we have the plant with its stamen and pistils, the egg cells and the pollen. There are two types of pollenization, one where the pistil is fertilized by insects carrying sticky pollen; the other by movement of the wind carrying the pollen. If I should believe my records, in attempts to cross trees, I might have a cross between a birch and an alder, in which the pollen is carried by the wind. I tried once to hybridize pines. I put some pitch pine pollen on the female flower of another species and seed resulted. I did this the second year and again I got seed. The third year I put bags on the female flowers before I could see them developing. Then I got no seeds. I believe that the pollen which had caused the seed to set in the preceding instances had come from the south for perhaps hundreds of miles.
There are times when the pollen of the staminate plant is all shed before the pistillate gets ready. Sometimes we have a plant that is self sterile. I have experimented with pollen from several different nut trees and also with the Norway spruce. Then again, there are abnormal cases; sometimes there is parthenogenesis. The jimson weed is the first plant which has ever been reproduced by parthenogenesis. Since that was discovered, an investigator in California has found a similar case in fruit developed without pollination.
One of the most important conceptions in heredity is its effect upon characters and factors. Take the Japanese bean here shown for example, one dark bean and one mottled. In the next hybrid generation we find three mottled and one dark. That is the familiar "three to one" ratio of Mendel's law. We believe now, that all, or at least a very large proportion of the heredity characters in plants of all kinds may be due to a series of factors; but the habit of growth of the plant is due to a single factor. We have the case here of a second generation of the weeping mulberry that I crossed with the white mulberry. As a result there was an average of three erects to one weeping one. Certain characteristics may be made up of the inter-action of a large number of factors. This will give a little idea as to the complexity of Mendel's law.
How do we get new characters in nature? New types are due to the rearrangement of previously existing characters, just as with the old-fashioned kaleidoscope, where you turn the crank and get new pictures. Another way is by the sudden appearance of new factors.
I wish to speak about one effect of hybridization, which is really connected with heredity factors, the vigor which occurs when we cross different varieties, species, or even races. In my experience certain types that have been naturally contrasted finally lose vigor, and after two or three generations the plant disappears. Then again I could show you cases where yields are greatly increased due to hybridity. These are established facts, not only as regards species of plants and trees but also as regards the human race. Hemy, in Dublin, who has done the best work in this line of endeavor, believes that many of our more rapid-growing trees are rapid-growing because they are hybrids.
To summarize, I have tried to point out the fact that diversity which we see in nature is real, and that it is brought about by two causes, namely, environment, and heredity. And that heredity is brought about by factors in the bodies of the chromosomes which are shuffled around like cards in a pack; they reappear in the same way that the cards will reappear. We have no means, as yet, of controlling the appearance of the factors, but we have two methods of getting new factors, as follows:
One—The finding of new things in nature; that, probably, is the very best method that can be used. The work of the theoretically planned project points out the tremendous importance of the exceptional individual.
Two—By taking the exceptional individuals, and by crossing them, you can recombine, although the results may be very complex, and obtain characters that are very desirable.
As ministers sometimes say to clinch the moral, I would say, "Seek earnestly that which is best and hold fast to that which is good."
THE PRESIDENT: Has anyone a question he would like to ask?
DR. MORRIS: In attempting to make crosses between juglans and carya we find often that the pollen of carya will excite the cell of the juglans but without making a fusion. What is the element of the male cell of the hickory which starts the female cell of the walnut into action?
THE SECRETARY: I would like to ask Dr. Blakeslee one thing; he showed the influence of the black walnut on the growth of the hedge, and he showed that something other than the effect from the black walnut had caused these plants to be dwarfed. Is that understood to be a fact?
DR. BLAKESLEE: No; some of the effect was due to the black walnut.
MR. HICKS: In some cases the trees get sick and die. I have observed many plants and trees growing close to walnuts and I can point out peach trees and other fruits planted close to black walnut trees which have been injured. I should like to see the question determined.
MR. O'CONNOR: On Mr. Littlepage's place it seems that some blackberries thrive better in the shade of the walnut tree than anywhere else.
DR. BROOKS: In West Virginia there is a locality where blackberries grow wild, and it is a matter of common knowledge that black berries will grow under the black walnut but that apple trees will not grow there. I have noticed that the best place to plant jimson seed is under the black walnut trees. I have no definite information about this but there is something in the influence of the black walnut trees.
MR. BIXBY: I have noticed at my place that cabbages planted under black walnut trees were somewhat stunted. I believe that it was the effect of the walnut trees growing so speedily that there was not enough nourishment for both.
THE PRESIDENT: The next lantern slide lecture will be by Mr. Reed.
MR. REED: (This lecture was delivered in a darkened hall where it was not possible for the reporter to take notes. However, the gist of the talk is here given).
The slides illustrated various methods of nut tree propagation, and that it is possible successfully to graft or bud nut trees at almost any time from February until the very end of the growing period. In working over large trees the first method in the season to be employed was shown to be that of the cleft graft. Following this, with large stocks, would be the slip-bark graft, or with smaller stocks, the chip-bud. The slip-bark graft has the advantage of being feasible at any time when the bark slips. Dormant scions are more often used with this form of propagation, although by no means necessary, as Dr. Morris has demonstrated that by applying a coat of paraffin over the entire scion and the cut surfaces of the stock, it is possible to use growing scions at almost any time when they can be obtained. The chip-bud is most successful during a relatively short period, beginning about ten days before the buds begin to swell and continuing until after the trees are practically in full leaf. From this time on the patch, or some other modification of the annular bud, is most commonly used.
In top-working, when the cleft-graft has failed, the patch-bud may be used late in summer, by inserting buds of the current season's growth in the base of the new shoots springing up from below where the cut was made in the stock for the graft, thus affording two opportunities for propagation during the same season.
The slides showed various methods of propagating the filbert by layering, and of propagating more difficult species by inarching. They were from a collection soon to be placed in the hands of the extension Service of the U. S. Department of Agriculture and of the various state colleges of agriculture.
THE PRESIDENT: We will now adjourn, and will meet in the room upstairs in this building at 10 o'clock tomorrow morning.