HOW TO HYBRIDIZE PEONIES

By A. P. Saunders

American Peony Society Bulletin No. 8, May 1919

Let us assume first that we had the task of instructing someone who knew nothing of the structure of a flower, as to what the parts of a peony bloom are, and how it is to be hand-fertilized with pollen from another variety.

We should, I suppose, take a single variety, as being the simplest, and show him first the petals, which, though so conspicuous, take no direct part in the development of the seed, but are there only to make the flower visible and attractive to insects. So, since we are to see to the fertilization of the flower ourselves, they may just as well be removed.

The next layer of structures inside the petals are the stamens. These are the pollen producing I organs, and each consists of a thread-like stem, the filament, and a yellow sac filled with pollen, I the anther. When the anthers burst, thousands upon thousands of microscopic, wheat-shaped pollen grains are scattered about, and any one of these may bring about the fertilization of a seed.

At the very centre of the flower are the seed pods themselves. There are generally three of these. They are called carpels, and upon the top of each of them is a sort of ridge; this is the stigma, and it is here that fertilization occurs. When a pollen grain is placed on the stigma, it sends out a process called a pollen tube, which penetrates down through the substance of the stigma into the pod itself, and there penetrates into one of the individual seeds. Through the pollen tube the contents of the pollen grain are emptied into the seed, fertilizing it and causing it to grow into a mature seed.

In cross-fertilization therefore, we must remove the stamens of the flower on which we intend to produce seed, and bring pollen from another variety with which to effect fertilization. The seed-bearing plant which receives the pollen, is called the female, and the one from which the pollen comes is called the male.

Our pupil will now want to know something of the technique of the process. This involves three steps, which I shall describe under separate headings:

STRIPPING THE FLOWER. The bloom on which pollination is to take place must first be "cleaned up." When this is done, nothing is left of it but the seed pods themselves. We first remove with the forceps all the petals, because they are of no use and get in our way; then we remove all the stamens, because if we do not, the flower will probably fertilize itself. Furthermore we must see to it that we get the stamens stripped off before any of them have burst. That means that the flower must be stripped early in its history. With double blooms containing few stamens or none, we are generally safe if we strip off the petals at about the time when the bud is unfolding enough to show the inside. With single flowers it is usually then too late; these must as a rule be stripped well before the stamens are visible. When you think the bloom might open out about the following day, tear off the petals and you will find a tight mass of stamens on the inside. Take a look at these with the magnifying glass, and see whether any have burst. If they have you will almost surely find pollen grains adhering to the stigmas. At the time when the anthers begin to scatter their pollen grains, the stigmas become covered with a sticky fluid to which pollen grains tightly adhere. Hence if you find any pollen grains there, give up that flower and take one not so far along.

When you get one that shows the stigmas apparently free from pollen, and with no anthers that have split open, clean it up, being very careful to remove every stamen. Then take a critical look at the stigmas and see that they are (1) free from pollen grains, and (2) sticky. If they are not sticky you should put a bag over the flower and work on it the following day. But assuming that they are in good condition proceed to the next operation.

GETTING THE POLLEN AND POLLENIZING. This is a simple matter if you have decided from what flower to take the pollen. Rather the best plan in my opinion is to have a glass vessel in which to place the anthers of the variety you wish to use as the male parent. When the biologists call a Petri dish, in a small size, is excellent, as it has a cover; but an ordinary little watch crystal does very well.

Pull off a few of the anthers and set them in the glass vessel, then tap it underneath so as to shake the anthers up and down. If they are in the right condition they will shake out a quantity of pollen on the surface of the glass. Now carry this back to the stripped flower, pick up some of the spilled pollen on the end of a very small sable brush, and dab it on to the stigmas until their sticky surfaces are well powdered over. If you have no brush, the best plan is to pick up an anther in the forceps, and rub it on the stigma until some of the pollen comes off; but you will find it all much easier and quicker using a brush. Our task is now accomplished, and all that remains is to protect the bloom from contact with any other pollen, and to mark it with a label.

BAGGING AND LABELLING. Very small paper bags may be had for almost nothing. One of these drawn gently down over the fertilized bloom and tied about the stem, will protect the bloom from further dangers, and may remain until the seed is ripe. So far as protection from other pollen is concerned, a few days would suffice for that; for the stigmas dry up very soon after fertilization has taken place, and when they are dry, fertilization is impossible. But if the bags are removed, there is danger in the autumn that the pods may burst and scatter the seed before it is gathered. I generally therefore tie the bag on tight and leave it until the time of ripe seed. A little peep-hole may then be cut in the top and the pod can be watched every few days until it is seen to open and disclose the brown seeds within.

For labels I use the little cardboard "string tags." They usually remain legible through the summer rains if the writing is done with a good black pencil.

The process of doubling in a flower is considered to be really a transformation of the other parts into petals. First the stamens are transformed, and finally the alteration may e«en extend to the carpels. In such cases it is often impossible either to get pollen from a bloom or to effect fertilization on it. Sometimes however when transformation has been almost complete so far as the stamens are concerned, a few petals may be found towards the centre of the flower, possessing thick yellow edges. If these thickenings are split open with a small knife blade or a pin, pollen will be found inside—not much, but enough to work with.

Different sorts show great variations as seed producers; some which apparently possess seed pods rarely if ever produce seeds. Duchesse de Nemours (Calot) is one of these. I have crossed on it several times and have never got anything. In some blooms it is almost or quite impossible to find any stigmas on which to place pollen. Richardson's Grandiflora is a flower where the process of transformation seems to have sacrificed everything to the production of petals; and so with many others. I have never been able to do anything with Therese; but Mr. Ringle of Wausau, Wisconsin, reported some time ago h-ving got a few seeds from it after repeated trials.

There are some varieties on the other hand that are conspicuously good seed bearers. One of these is Primevere. I think I have never found any pollen on it, but I use it every year as female parent and it sets such grand pods of seeds that the stems have to be staked to keep them from being broken by the weight of the seed. I mentioned in Bulletin No. 5, a bloom of Primevere from which I have taken 61 good seeds.

Other good female parents are Venus, and Marie Crousse, neither of which ever show pollen of their own. James Kelway, M. Martin Cahuzac, Adolphe, Rousseau, are also good seed producers, but they all have stamens, and should be carefully examined before being used. The Japanese blooms almost always set seed well; and though it is very unusual to find any free pollen on them, some may almost always be had by opening up the thickened edges of the central petaloids.

A curious case is that of the Wittmanniana hybrid, Le Printemps. It happens to be the only one of these hybrids in my garden of which I have large and robust plants. It is a single, with stamens and carpels apparently well developed. Yet in spite of repeated efforts through several years, I have never had a fertile cross either on the plant itself with other pollen or on any other sort where the pollen of Le Printemps was used. It is, I suppose, a sterile hybrid.

Generally speaking the singles yield large quantities of seed. Most of them came themselves out of double strains, and from their seed there comes a large percentage of double progeny. Hence they ought to prove pretty satisfactory as seed parents for crosses.

Last year I had a strange disappointment in connection with P. lutea as female parent. I had some crosses on this species using pollen from Chinese peonies, and was rewarded with half a dozen immense pods of seed. When the pods burst, there they were,—two or three dozen big black glossy seeds. But when I got them out, I noticed that they gave a little under pressure between the fingers, and on breaking one open, I found that the seed was nothing but a tough shell, there was nothing inside. And so it proved with all of them. Now generally speaking, when a cross fails the seed pod soon shrivels and dries up, but these had all the appearance of the most successful crosses. What sort or degree of fertilisation was brought about here that would produce big seed pods, and fine looking seeds, yet all only a hollow pretense?

I had spoken of several little implements that the hybridizers needs, and now for the sake of those who do not live in large cities, I shall tell where these things may be had.

Magnifying glass. Get what is called a doublet magnifier, giving 14 diameters magnification. The' cost about $1.25 to $1.50, and may be had from the Kny Scheerer Co., 404 West 27th St., New York, from the Scientific Materials Co., Pittsburgh, Penna., or from any scientific supply house. In using, tho glass must be placed very close to the object, and the eye almost touching the glass.

Pincers. I like what are called Denton Forceps, but any small sized pincers will do. Carried jin, most drug stores. The Denton Forceps may be had from the Kny Scheerer Co., for about 50 cents.

Petri Dishes or Watch Crystals (Watch Glasses) may be had from either of the above firms. Petri Dishes, 2 inch, about 20 cents each; water glasses cheaper.

Small Sable Brush, at any art store or large stationer's.

Tags for Labelling. I use Dennison Marking Tags 36B. They are of a good comfortable size.