The Horticultural Review and Botanical Magazine 4: 136-138 (Jan 1854)

Hybridizing. — Saving Pollen.

MR. BEATON, one of the leaders of that excellent and practical journal, the Cottage Gardener, when considering the subject of Hybridizing plants, said, many years ago, that he believed the pollen of Rhododendrons might be gathered on the Himmahlayas [sic], and sent over to fertilize the varieties in cultivation, so as to produce new hybrids. He appears to retain the same opinion, and makes some very sensible suggestions which will be read with great interest, not merely by the practical gardener who is pursuing this higher department of his art, but also by the student of vegetable physiology.—Eds.

We have numerous accounts on record of seeds having vegetated after long periods of rest, away from atmospheric changes, after being boiled for different lengths of time, and after resisting the pestilential influence of sewer and soil-drains for many years. Plants have been raised from seeds which ripened in the herbarium of the botanist, and remained there for a lifetime; and there is hardly any other way of transmitting the seeds of Ferns from one country to another than that of cutting off specimens, or pieces of the Fern-leaves, before the seeds are quite ripe, to dry them, and then pack them where no moisture will reach them, and they are safe for many years, the dust-like seeds of Ferns being even more tenacious of life than the larger kinds of seeds; but to retain its power, it must be in the seed-vessels, and on the leaf which bore them, and the leaf must be gathered and dried like hay, before the seed-vessels are ripe enough to open and discharge the seeds.

In the same way, and under similar circumstances, we have presumptive evidence that pollen may be gathered, and harvested so as to retain its subtle power of impregnation for any definite period, or, at least, as long as Fern-seeds retain their powers to vegetate. This is a new field of inquiry into which we would lead the young gardener and the amateur.

The improvement of races of plants is not destined to stand still more than other improvements, and nothing would tend more to the speedy termination of an experiment than that we had control over the supply of pollen, so that we might use it when and where it was most convenient to ourselves. The power which we now acknowledge in conducting experiments, extends no further than getting the two parents into flower at the same time, or within short periods of each other. In anything beyond that, we are, at present, powerless; but we see no just reason why we should be so confined with pollen more than with Fern-seeds; preserve them, or say, at once harvest them, exactly on the same principle, and the one will keep just as long as the other. * * *

We have had reports of failures in trying to keep or harvest pollen from Australia, India, North America, and from many people in this country, but from none of them have we heard one word about the process of ripening and drying pollen; therefore, we shall assume that no one has yet mastered the seeming difficulty of harvesting pollen for future use, and that the failures recorded were not due to the impracticability of the thing, but rather to the want of a knowledge of how pollen ought to be harvested, and that want is what we now propose to supply. Pollen, fifty years old, in a herbarium, was found, under a microscope, to yield to moisture exactly as fresh-gathered pollen would do — the little bags distending till they burst; the matter discharged differed in no way from that from a recent anther. The seeds of Ferns have been brushed off from a specimen dried for, and kept in, the herbarium for more than fifty years, and produced plants. Who can describe the difference in size and weight between a pollen-grain and a Fern-seed; and who can believe it possible that the seed would keep fifty years, and that the pollen-grain would not, under similar circumstances?

The failures in saving pollen arose entirely from want of thought in the harvest-men who undertook the experiment; they allowed the anthers to become ripe before they gathered them, or so near to ripeness that they opened during the process of drying. Now, if we allow a Fern-seed to break its case and get into the open air, or the anther is allowed to open its valves, as the case may be, we might just as well attempt to lock up electricity as to secure the Fern-seed, or the pollen-grain, from destruction. The case of the Fern-seed must never open until it is rent asunder by the swelling of the seed itself, under the bell-glass of the gardener, on the damp sand. The anther must be equally guarded from every influence that would excite it to open until it is wanted, or rather its contents, for the stigma of the recently opened flower, All that we have actually proved on the subject is this, that if we extracted anthers and stamens long before the anthers were ripe, that the pollen in them would ripen, and be in use, and fit to cross, after the lapse of six months; and that pollen gathered when ripe and flying out of the anthers, though kept with the greatest care, would not fertilize the stigma of the parent plant at the end of a month. We believe the driest atmosphere we can keep in our rooms and drawers is far too moist for the preservation of pollen for any length of time after being actually exposed to it; and we also believe that an anther would keep as long as a piece of bladder under the same influences, and that it is as impervious to moisture as the bladder, and, therefore, as capable of preserving pollen as is the seed-vessel of the Fern in retaining the vitality of the seed — a fact that no one now questions.

If the flower of the Geranium is picked off as soon as it opens, although the anthers may appear to be only half ripe, there is sufficient moisture in the flower to feed the anthers and cause them to burst in two or three days. Therefore, if it was intended to dry that pollen for preserving, it could not be done, as no method could be adopted to save it if once it is in contact with the air; that flower was too far gone to be harvested for pollen, and it would be much about the same with nine flowers out of ten from other plants.

Then, it follows, that when we wish to make dry specimens of flowers, with a view to save the pollen, we must gather them a short time before the flower opens; or when there is more than one flower on a stalk, and they are known to open in succession, it will be as well to let the first of them just open before you cut the stalk, and let it take its chance; if we can get it and the anthers dried in such a manner as that the latter do not burst, so far so good; but, if not, the loss of the former flower will not be much, and we can reckon on some, or all the rest, to ripen the pollen without reaching that point of ripeness when the anther should burst.

Here we are met by a wise provision of nature, which is familiar to any one who has been in the habit of dissecting flowers, and which greatly assists us in this work. The anther is the first part of a flower which comes to its full size, the stamens lengthen out very gradually, the petals no less so, and the stigma is hardly ever up to its full size so soon as the other parts; but the anthers, on the contrary, are of full size when the flower is only in the bud. In some plants they are full-grown ten days before the flower opens. Wheat, for instance, is impregnated by its own pollen before the top of the ear issues from the sheath, and before stamens come into existence, or nearly so; therefore, it is impossible that one kind of wheat should naturally fertilize another wheat in the field. The moment the wheat pollen is shed, the stamens begin to lengthen, carrying up the empty bags on their summits, till, at last, they push them right into the open air; then the farmers believe the plant is in blossom

We have met with a hundred instances in which the anthers were in full size, and all but sessile; that is, without a sign of stamen below, while the flower is a mere bud. To cut a full-sized anther, at that stage of the flower, would give one no signs that anything like dry dust should ever be formed by it. It is a solid mass of tissue, apparently like any other soft portion of the plant. Now, supposing that one of these flowers were cut off ten days before the pollen would be ripe, and that it was dried very slowly, after the manner of specimens for the herbarium, if there were sufficient moisture in the stalk and surrounding parts to keep the anthers from shriveling, there is no question about the pollen ripening during the process of drying. The full-sized anther requires no more room when the flower is quite opened than it occupied some days before; hence, the greater facility of getting the pollen well-ripened after the flower is cut, without causing the anthers to burst open.

Suppose, now, that we have a truss of Geranium flowers well up in the bud, dried, and ready for the herbarium, with the pollen ripe, but the anthers not likely to burst or open; is there anything in reason, or philosophy, which can contradict our surmise, that that pollen may be kept in that state for many years, and be as good when the anther was cut as it was the first day? We think not.

The next question is about the best way to dry the flowers; and here it must branch into wide-spread diversities. Some flowers, with thick substance in the parts, say a Gloxinia flower, will require to be dried as fast as it can safely be done, or the great store of sap will, assuredly, run the anther to the bursting point before all is sufficiently dried. Another, say some slender Heath flower, with hardly any substance in it, or round about it, in the leaves or the shoots, must be dried as slowly as possible, in order to give time to the full development of the pollen; and all intermediate flowers must be dealt with according to the best of our judgment, until by practice, we come to understand more of the subject that any one can lay claim to at present. What we have to bear in mind, is, that if the anther once opens there is no more safety to the pollen; that the juice in the parts is sufficient to ripen the pollen after the flower-buds and flower-stalks are separated from the plant; and that it is not safe to trust to the anthers getting too near the ripe stage before the flowers are cut off, lest they go on to bursting before the specimen is dried. If all this is kept in view, the rest, about the length of time, and best ways of drying, will easily be found out in the course of practice.

We know of nothing now to be ascertained, from the whole circle of botany and gardening, of so much importance to mankind, as the affirmative of all these suggestions; for, let us be understood only as suggesting the probability of the subject being within our reach.

The way they dry botanical specimens for the herbarium seems as good as any for drying pollen specimens. The first day or two the specimens are spread out, and held between sheets of blotting-paper, in a book, the sheets, or the position of the specimens being often changed, so that the blotting-paper does not get wet or damp. After a certain degree of drying, some pressure is applied, but this we must not indulge in too far for pollen-drying; the least weight might squeeze a ripe anther to the bursting point, when all would be lost. When the process is complete, the flower-buds, the flower-stalk, and the branch, if any, ought to look as natural and free from stains as an ear of corn, or a grass-stalk from the hay-rick. There is hardly a plant known, of which a dried specimen is not kept by some one. Weeds are kept with as much zeal as the most gaudy flowers, and new names are now often determined by old specimens that have been preserved hundreds of years. It was from an old flower thus dried that we first took up the idea of saving pollen; on the application of moisture to the old dried pollen it exhibited all the symptoms of vitality, under a lens, that fresh pollen from the garden could do; and knowing the vast stride in the improvement of races, which pollen ready at all seasons would give us, we are anxious to press candidates into the field.

Suppose, again, that we have dried pollen at hand, and that fresh flowers are ready for dusting — take the dried flower, and, with the point of a pin, tear the anther open, then stick the pin through it, and carry it on the point of the pin to the stigma to be fertilized, and draw it two or three times across it, then give your hand a gentle touch to dust off the remaining part of the pollen, and the work is done. The plant may require to be kept out of the draught for some hours, as the old pollen may have to lie longer on the stigma than fresh pollen, before it effects the mysterious process. Who that has a Japan Lily now in bloom, that would not wish to have a ripe anther of some spring or summer lily to try his first experiment in crossing? Autumn and spring Crocuses, if they could thus be crossed, would give us flowers for the whole winter, and so on through all the families in the catalogue.

There is one more branch of this subject, a most simple one, and yet it seems to have been a stumbling-block to every cross-breeder, [hybridizer] here and abroad, who has recorded his exploits. Notwithstanding the utmost precaution in guarding against the access of its own pollen into a flower — and even going so far as forcing two plants in the spring, in order to make more sure of a cross — they tell us, one after the other, that the produce was in nowise different from a natural seedling. We have no record, however, from any one, of how he destroyed the natural pollen, more than we have from those who failed to harvest pollen, how they managed, or rather mismanaged the experiment; therefore, we must presume that they merely extracted the anthers, the moment the flower opened, or just the day previous to the opening, and let them (the anthers) take their chance. Here is just where the mistake lies—the anther, or rather, the pollen, is all but ripe in any flower when that flower is fit to open—or, if the extraction is done some days previous, we have seen that the juice in the stamen, or even in the anther itself, may be sufficient to ripen the pollen after the anthers are cut off; and we know the least breath of air will disperse ripe pollen in clouds like dust.

Suppose, then, that you had extracted all the anthers from a Geranium flower this morning, and let them drop down on the surface of the pot or border, that was not the least security against that very pollen entering the same flower from which it was extracted, and neutralizing the effect of another pollen; the air, or wind, the bees and ants, had the same power, and the insects the same will, to disperse the pollen from the fallen anthers, as they had when the pollen was allowed to ripen side by side with the stigma. We have often seen an ant carry a discarded anther a long distance in its mouth, up and down, through all parts of a plant, across the stage, and off to its nest. We never did see an insect carry up the pollen from a fallen anther back to the flower, and actually dust it on its sister stigma; but we see nothing to prevent the possibility of access in some such way, unless the anthers are actually squeezed to death between the finger and thumb the moment they are cut out. One can never rely on success if a single anther has dropped where we cannot find it, so as to have it destroyed on the instant. The fact of letting a single anther escape destruction accounts, plainly enough, for the failure of any single experiment.

Bidwill: Vitality of Pollen (1850)

Beaton bibliography