Hort and Cottage Gardener 232-234 (June 25, 1861)
The bustle consequent on the May meetings has prevented me from giving sooner more explicit answers to Mr. Darwin on the subject of crossing.
I did not comprehend his meaning about the natural crossing of varieties, which is familiar to the farmer as to the gardener. I put the cart before the horse, and understood natural varieties crossing among themselves, instead of artificial varieties crossing naturally. Artificial varieties in the flower garden will cross naturally with as much freedom and with the same results as in the farm Turnips or the garden Cabbages. And there is an error at that point in the reasoning of some of our best scientific writers on plants. They say the effect of such natural crossing of varieties is a reversion to one of the original types; but I know of no instance in which that theory is sustained by the result, and I endeavoured for some years to force Calceolarias, and Fuchsias, and some other kinds back to their originals with the same unvarying consequence.
As far as I can see, I cannot believe that reversion will take place under cultivation. I know that "improvement," as we call it, among flower garden races has its origin in cultivation and not in crossing; and as a consequence I take reversion, if it is possible, to be the effect of want of cultivation. At all events, I am perfectly clear that all our skill could not now make one Calceolaria plantaginea from all the sorts under cultivation.
The real effect of the natural crossing of artificial varieties is exactly the same as we know to be the case in every instance in which we apply pollen—the pollen of the strongest, or coarsest, as some would say, takes the lead. There are, indeed, very few men who ever dream of the pollen of one individual flower being of two distinct natures, and capable of originating two distinct races of plants from one and the same application on two mothers, but it is so most certainly. But let me be understood. A is a breeder from which I want seedlings, and B is the father I wish for. Now, I shall take two As and one flower of B; out of the qualities of the pollen of one flower of B I shall produce two distinct races. I have done it a score of times, and I told the secret and showed the way of manipulation to Dr. Hogg, three years since, in my own garden; but I hope he will not say exactly what that way is till we see if we cannot, by some such means, raise the spirit of gardeners from commonplace things to the higher pursuits of cultivation by crossbreeding, the spirit of the age being all but dead on that one subject.
"How do you know the strongest plant influences the progeny?" I may be asked, and if I have nothing to prove the fact, I may be told the thing is a mere fancy. But the breeders of animals, from the canary to the racehorse, can give you the tips and downs of the crossing of their respective races without the samples to prove what they advance.
I had hoped his majesty of the cross-breeders would himself have answered Mr. Darwin about the Anemone apennina and the Mathiola incana and glabra. He is a reader of this work; and if I petition his majesty, who may have been from home on "drill husbandry," he, or his gardener, may see it without my writing a private letter.
There is a prescription for proving in two months the assertion about one kind of pollen taking the lead of four other kinds on the stigma of a Geranium. The leaf invariably goes after that of the pollen parent in the Scarlet races of Geraniums. Cross Tom Thumb with a Horseshoe kind and the seedlings are all horseshoed in the leaf. Cross the deepest-marked Horseshoe kind with the pollen of Tom Thumb, and all the seedlings are plain-leaved. But to be perfect, the two kinds should be forced into flower before others of their kind had opened their flowers, for fear of admixture. Now, knowing that feature may be relied on, take Baron Hugel, the easiest to cross of all the flower-garden kinds, as it never has an anther of pollen, nor refuses to breed freely with every other kind of the same race. Put the pollen of Tom Thumb on four of the five divisions of the style, and the pollen of the Cottage Maid, or any other equally coarse Horseshoe kind on the fifth division, and your seedlings will be all horseshoe-leaved. That proves one side of the question. In two months the seeds will be ripe, and up in the third, or rough leaf, showing the characteristic of the strongest or coarsest parent. But mark the four divisions with one or four kinds of the Horseshoe race called Minimums, and use Tom Thumbs on the fifth, and all the seedlings will be plain-leaved.
That is the simplest way I can suggest, and the surest is with the single Hibiscus rosa sinensis; but it takes five years of the best cultivation to get all the seedlings to bloom, and some of mine did not offer to do so before the seventh year. Ten years are a short period in the experience of a cross-breeder of any race. When Mr. Darwin says (page 211), that "experiments are tedious and very often fail," I hope he did not mean the application to gardeners, for of all men gardeners have most need of the proof by experiments. It has been by the easy method of pinning one's faith to the sleeve of some priest or prophet, that the spirit of inquiry has been brought down so low on the gardener's scale that electricity itself seems now not able to move one of his muscles out of routine and hand-to-mouth knowledge, be he never so wrong.
From what Mr. Darwin says of his experience of flowers fertilised by their own pollen shows how very differently botanists and gardeners look at the same flower. Has he, or any other botanist, remarked how flowers in the composite order are provided with the means of self-fertilisation? and yet were it not for the proximity of the florets there would be most chances against fertility. Botanists do admit the alliance between our little blue Lobelias and their Dandelions, though almost grudgingly. But a cross-breeder sees no difference between a scarlet Lobelia (L. fulgens, say) and a Chrysanthemum—at least, I do not find any difference between them for my part of the examination. Now, if all the composite flowers had their florets scattered up and down on a long stalk, instead of being crowded into one head, and bound round with a hygrometric belt, to which most syngenesious involucres may be likened, the chances are that few seeds could be obtained from them.
There are hard upon ten thousand species of composite plants, and by a rough estimate the florets of such flowers may be put down at fifty to each flower; then if we take but one flower of every species of composite, and reckon every one of its fifty florets a complete flower of itself, as it is in respect to the process of the cross-breeder, we shall have half a million of flowers in one order, in which provision is made that none of the flowers can fertilise itself: therefore, when I said that not a flower in a thousand is fertilised by its own pollen, it was only as a drop in the ocean as compared with nature. I said I had very little knowledge of crossing composite flowers; but from what I saw as an insuperable difficulty against crossing them, I concluded that in that order the parts for crossing are all laid down on one principle, however widely that principle might vary in different sections of the order—and the principle is, that no floret is fertilised, or is intended to be fertilised, by its own pollen. But to make this clear to the amateur and young gardener, for whom all our writings are more especially intended, let me explain the process for fertilising a composite flower.
The flower of a common Daisy on the lawn is a congregation of flowers on one common head, and I have assumed this congregation to be fifty in number. On a large scale the flowers in the centre of the Daisy might bo likened to Polyanthus flowers. If they were all cut just below the pineye, the pretty parts gone, nothing is left but the bare tubes; and if these tubes were now sealed over, and the thread on which the pinhead rests is just inside the sealed tube, the style or thread is just like the finger of a child in a glove, but the thing is more complicated. Bear in mind that the finger of the child represents the style or female part, and know also that the top joint of the glove is lined with an extremely thin lining, and that on the inner surface of this lining stand the anthers with the pollen or male part. The top of the finger, then, stands under two covers—the glove finger and the lining, and the pollen is round the top of the lining. Now, the style (finger) grows up and splits the lining first; then the finger of the glove gives way, and the point of the style is out in open air at last; and if there was a pinhead on the point, the style of all composites at that stage would look just like the little head in the centre of a pineye Polyanthus. But the way the pollen gets up to fertilise the top is one of the greater characteristics of this great order; and strange to say, no botanist that ever I read explained how the crossing or fertilising is effected.
The way is very curious. There is a raspy surface, or a gummy surface, or a feathery-like surface, round the top of the style, and for half an inch, more or less, according to the kind, under the point; and when the point is forcing its way through up through the lining and splits it, the pollen is scraped off the lining by the raspy surface of the upper part of the style, or by the feathery surface, or the pollen sticks on the gummy surface and is carried up right into the open day. A casual observer might think the pollen is then doing its own work. Not at all, the process is yet more curious. The pollen is then only exposed to the open air, which seems essential to its acting properly. Most of the flowers which I have examined were some common garden plants, and they held the pollen airing for twenty-four hours, some more, aud some less, and no more than two rows of florets all round the outside of the centre pushed up the styles the first day. At the end of the twenty-four hours the stigma or point splits into two parts, and they roll back like as two of the five divisions of a Geranium style. How is the pollen, then, to get to the upper surface of these two divisions or horns? It never gets there at all, and unless other fingers or styles were to push up near the first set with their pollen, the first set could not be fertilised, as their own pollen could not reach the spread of the horns. It is the pollen of the second set of risers which fertilises the horns of the first set. Two or three florets in the centre, or very near it, are the last to rise, and as their own pollen cannot reach them, and there are no more to help on the good work, these few florets are always barren of seeds; or, if there is a semblance of seeds, there is no life in them.
There is no end to the shapes which the horns of the style assume in composites—some are as in the Pink and Carnation, some like barbed shafts, some like a pair of tongues, and so forth; but in all composite flowers the style splits into two parts when it is ripe for the pollen, and every style in all the endless form of composites carries up the pollen with it, and airs it before that style is ripe for the final process; and if there were no insects or wind to disperse or disturb the pollen, its own pollen could never fertilise one floret out of all the composite order. The lining round which the anthers stand, or rather the pollen, is called the syngenesious membrane, the membrane being the edges of the anthers cohering, and the word is equivalent to Hymenocalhs.
When I mentioned last winter that we should get all the Gazanias into one border, and give them orchard-house protection in order to be able to cross them, I intended, as I have just done, to explain the nature and the extreme difficulty of crossing any composite flower, and I am not aware that a single instance of any one having really gone through the process is on record. When I said I knew no difference between a Dandelion flower and the flower of a Lobelia in the ways of crossing, you can see now what I meant, which was merely a single floret; the anthers of all the Lobelias cohere into a united membrane, or lining in the tube, of the flower (the floret), and the style has to pierce through that membrane and disperse the pollen, just as in the floret of a composite, only that oftener than not the fringe which encircles the stigma of Lobelia keeps some of the pollen in readiness for the style, and there is little fear of its reaching the right part at the proper moment.
All the best garden scarlet and crimson Lobelias resist every effort at breeding after the second, or, at most, the third generation. I never could answer the question, Is air essential to the proper acting of the pollen? Most of the Campanulas are fertilised without airing the pollen; and it would seem from Mr. Darwin's experiment with Leschenaultia, which is highly interesting, that the pollen of that family may be aired before it fertilises, if not it must be aired before it is fit for use. But there are two obstacles to that view of the case. If it must be aired, it has to remain in the cup, or indusium, for three weeks or more after being otherwise ripe and shed before it can get to the air, which seems too much roundabout for a process of Nature—Nature's plans being always more simple than that in detail; and secondly, when insects disturb the pollen, as Mr. Drummond told of, its fertility seems gone altogether, for we never had a supposed natural cross from the locality of the family. A cross-breeder would expect more wildings from this one family of two species than from the largest family of Australian plants. A breeder would call all the purple and yellow kinds one species only, and the blue the other. Then yellow and blue in one family, and that family having never yet branched off into endless forms, is only one more difficulty among the thousand which already beset the path of the cross-breeder.
I can answer Mr. Darwin's question about the "self" coloured Pelargoniums. I crossed a score of such flowers, and found no difference in the seedlings. Mr. Catleugh told me he tried them for seven years running, and never obtained a "break;" but I did not notice in what part of the truss a single "self" appeared. The more usual way is for a whole truss or a whole plant to have all the trusses at one time all of one colour. I once had one flower of a genuine wild species of Cape Pelargonium—a most hideous-looking flower, in a truss of one of the greenhouse bedders, I think Touchstone or King Rufus.
Of course, I do not mean to make a secret of how two races of Pelargoniums could be made out of the pollen of one flower; but I shall give time for young gardeners to exercise their wits in trying to account for such a thing or how to do it. But the first, and the last, and the centre flower of Pelargoniums, come all alike under the like circumstances; and if you cut off the stalk and a whole truss when you see the seeds have been fertilised, and are able to ripen them under a glass case, as I have done repeatedly, you will find no difference in the seedlings from another truss on the same plant which has been fertilised by the same pollen.