The Cottage Gardener 2: 143-145 (June 1849)
In my last letter I said that I never attempted to cross-breed roses, but that I would try a few experiments in order to enable me to explain the process more simply in this article. I have now done so, and I may safely affirm that had it not been for this anxiety to dish up a nice story for THE COTTAGE GARDENER, I should have lost one of the greatest treats I have experienced for many years in the examination of flowers. If I have cut up one flower, I am within the mark in saying that I have dissected many thousands, and out of that number I do not recollect of having met with a single instance where the interior of the young seed vessel was so arranged as in the rose, and I was not aware that such conformation as there presented itself was to be met with in the whole vegetable kingdom; but more of this another time. Every school-boy may be said to possess a certain knowledge of comparative anatomy as soon as he is able, in his own way, to dissect pomologically, if there is such a word, and compare on his palate the differences which exist between a strawberry and a cherry; a fact which I learned from the first botanist of this age, who, on his way to place two of his sons at a celebrated academy, called in to see a rare collection of plants then under my charge, and after seeing all the "new things," the conversation, naturally enough, turned upon botany, and amongst other questions I asked him if the two young students wore likely to turn out "chips of the old block?" "Why, yes," he replied, adjusting his spectacles, "both of them have already acquired the most essential point requisite for an expert botanist; for," he continued, speaking botanically, "each of them has a good practical knowledge of comparative anatomy;" meaning, no doubt, that they made some proficiency in cracking nuts, eating apples, sucking peaches, and all that sort of anatomy. Our knowledge of flowers, and of the incipient fruit which accompany them, must be limited indeed without some process of anatomy, if only to split a rose into two or four parts with a common knife, as I did the other night. A hybridizer may cross and re-cross his flowers till doomsday, but, unless he makes himself familiar with the different parts which compose a flower, their various arrangements, and the functions allotted to each, he is deprived of half time pleasure and interest which the subject never fails to impart. Therefore, this involves a certain smattering of botany, the slightest knowledge of which would also add to the zest of dissecting a flower for the first time.
Now, with only the most superficial knowledge of these things, I began last week to dissect flowers of the various sections of the rose, from the single wild brier, through the various stages of semi-double flowers, on to double and the most double ones. From this summit I descended on the opposite side through all the gradations of that malady which we call "green eyes," or centres. I had eleven flowers in all, and most of them I had to split into four parts, and after two hours' examination and comparison of all the parts, although, as I have said already, I never crossed or opened a single rose before, unless I can show you how best to go to work at once with them, I shall engage to forfeit my nationality, the severest punishment a highlander can undergo, and get through it with a safe neck. I believe I have read the substance of all that has been published on time subject of morphology—a science of recent birth, and which explains the nature of vegetable monstrosities, of which the green centre in a rose flower is a sad but familiar instance—and from all this reading I did not obtain so clear a view of this new doctrine as from the dissections of which I am now writing.
Procure a quantity of green-centred roses tomorrow; let them be in different stages of transformation, from the changing of the pistil to a rough grey surface, up to time full development of a green leaf; cut them into four pieces, and unravel the pistils one by one from the central mass in which they are all jammed together; compare these in all their stages with the perfect pistils in the centre of a single rose, and you may gain a tolerable insight of the rudiments of morphology, and you may see in reality a more strange metamorphosis of parts, and their progress in time transition state, than the rich mythology of Greece supplied to the pliant quill of Ovid. The fact before you of a lady of the bedchamber, or a maid of honour to the queen of flowers, being transformed into a green-eyed Susan, or to a perfect roseleaf, is even more singular, though not so sad, than that of the lovely Thisbe being turned into a mulberry-tree after her tragical end with Pyramus, her unhappy lover, whose lutes every schoolboy has sincerely and most affectionately lamented.
Now procure a single rose, the blossom of a wild brier will do, and let us examine the parts in succession. In all roses the flower is seated on the young hip, or seed vessel, and every seed vessel, from a rose hip to a full ripe peach, is called by botanists a pericarp, a word you will easily learn when I tell you that the meaning of it is "round the fruit or seed," and is taken from two Greek words, peri, about, and karpos, a fruit. Therefore, an apple is a pericarp, and so is a pear, and a peach, and, in eating these, we do not eat the real fruit of the tree, but the pericarp of the fruit, for the seeds are, in reality, the fruit. The rose, then, is attached to the end of the pericarp, and we must have them both. In most flowers the different parts are arranged in four whorls, or rings round the stein as a centre. It is so in our single rose, the outside covering or calyx is one whorl then the single row of petals is the second; the third whorl comes next, and is composed of an indefinite number of stamens, or "gentlemen at arms," as they really are, with powdered heads, in the shape of dusty pollen; and the centre whorl is composed altogether of pistils, her majesty's maids of honour, all of whom—and they are many—are desperately tight laced by the contraction of the mouth of the pericarp, through which they issue into the presence and very centre of their lords. Here, then, we have the pericarp, calyx, petals, stamens, and pistils. The two last-named are called the seed organs, and the calyx and petals, floral envelopes. The stamens in the rose are very numerous, and they also are arranged in whorls. In the progress of a single to a double rose, one or more of the whorls of stamens are converted into petals, and, according to the number of stamens so converted, is the degree of doubleness of the flower; and in a perfectly double rose all traces of the stamens have disappeared. The beauty of the rose, therefore, is owing to the transformation of the male organs into beautiful rose petals; the pistils, or female organs, may or may not have retained their original power of fecundation, and, with the assistance of ripe pollen from another flower, will produce a cross offspring, and the hand of the cross-breeder might easily effect a cross at this stage.
If things would continue in this condition, we should have no cause of complaint or disappointment, for, from my slight acquaintance with the rose as a breeder, I am led to believe that it is from flowers of this stage of development that we are to look for success in crossing them. It is not to be supposed, however, that every double rose, even with the female organs in perfect development, will produce seeds, although, from not having any experience in crossing them, I cannot speak positively to the fact; I merely reason from analogy with other families with which I am well acquainted. for I often find that plants, belonging to families that have been already extensively crossed, like the rose, with all their organs of reproduction apparently in a perfect state, are yet incapable of breeding, or, in other words, are absolutely barren. The cause of such barrenness is a total mystery to the most learned, for I have had conversations and correspondence with main many eminent physiologists on this very point, and with M. Decandole, the present professor of botany at Geneva, among the rest. When he was in England, in 1837 or 38, I forget which, he called where I then resided, and he conversed freely on this subject, and proposed a correspondence, but, though he speaks English fluently enough, he would only write his letters in the French language, and I was obliged to relinquish the pleasant task, as I do not understand the French language. He told me, however, that his father—now no more—whose shoes he is now fast filling, and who was the first authority in all matters relating to botany and physiology, could never fathom the mysteries of cross-breeding so far as to have been able to lay down safe rules for its application. Therefore, as I have said already, we must work on step by step. No doubt all our great nurserymen could, from their extensive experience, tell of many fine roses that are sure breeders, and of others, equally good, from which no seeds can be obtained. A list of such plants would be a welcome article for ally of our gardening periodicals, and to none more so than to THE COTTAGE GARDENER. In the absence of such a guide, all that I can offer at present is to point out the necessary conditions in the stamens and pistils of a rose to render them fit subjects for experiments.
I have said that it is not necessary that the stamens should be present, it is indeed safer that they should not be so, except in the form of petals, thus rendering the flower perfectly double, and therefore having no pollen of its own to interfere with the experiment. But it is essential to success that the pistils be in a perfect state, which has not been the case in every instance in those roses I have examined. To be in a proper state for the pollen, they should be perfectly smooth and fleshy, with their tops (stigmas) moist with a clammy fluid, which is their element of fecundation. The rose which is made choice of for the other parent cannot be a perfectly double one, as in that case it would, as we have explained, be without stamens, and could yield no pollen. But the more double it is the better, provided it has a few perfect anthers charged with pollen, which is easily known by their powdery appearance. The pollen of the rose is of a lighter colour than is generally the case with other flowers, and is ripe when it will fall from the anthers in the form of dust on the least touch. The best and easiest way of applying the pollen to the pistils is to cut away the petals, leaving the stamens attached to the top of the pericarp, (that top is called the torus.) Now, with the pericarp between the fingers, draw the stamen gently three or four times across the clammy stigmas of the pistils, and, if the pollen is quite ripe, it will adhere to the moist stigmas, and the work is finished.
After a while the pollen grains will imbibe so much of this fluid as will cause them to burst, and discharge their contents; then a chemical action is supposed to take place; at any rate, the mixed juice circulates through the pistil, the bottom of which, in the rose, is attached immediately to the ovary, which incloses the embryo seed. Now, what most surprised me was, that these ovaries, which, in reality, are the coverings of the future seeds, were placed inside the hip, or pericarp, in a widely different manner from the generality of such cases; but this is a question of no moment to the cross-breeder. There are various conjectures as to the mode by which the pollenised juice—to coin a new word—finds its way to the ovule or embryo seed, and, in my hurry the other day, I said that this compound juice circulates in the same way as the ordinary sap, but the truth is, the whole process after the union of the pollen is a perfect mystery. It is true that some have asserted that the contents of the pollen is formed into tubes of extreme fineness, and in that shape slides down through the style (stem of the pistil), and so, by means of the seed cord, or placenta, passes immediately into the ovule. But when we reflect that in pendulous flowers, like those of a fuchsia, for instance, these same tubes would have to slide perpendicularly upwards, we cannot readily yield assent to such an extreme doctrine. Let us rather assign this part of the business to the care of the philosophers, who, no doubt, will settle it right enough some day or other. If we could but succeed in originating a double yellow perpetual moss rose, we ought to possess philosophy enough to rest satisfied with our own part of the business, and not interfere with that which is the lawful province of our betters.
The next division of the subject belongs more to morphology than to hybridization, but let us see whether or not we may derive some useful hints from this part also. As for myself, I am tempted almost to believe that if we could fathom the cause of the monstrosity of green centres in the rose, it might throw some light on the reason why the French growers have hitherto excelled the English in the production of superior new seedlings, and if so, it would prove a good hit. There must be some cause for every thing, although it may often, as in this instance, be difficult to discover it. We have already traced the progress of development from the single brier to the full blown rose, with the parts perfectly organised, only that the stamens have been converted into petals, all this being the effect of care and cultivation; but no sooner have we arrived at this perfection than the rose makes a retrogade movement, according to our ideas of a perfect flower, but no doubt in accordance with some natural law. The next move is in the pistils. Out of these, and these only, are the green leaves, which disfigure the centre of so many roses, formed; thus clearly showing than the nature of the pistils is very different from that of the stamens, at least in the first stages of monstrosity. As soon as the pistils begin to turn into green leaves, their legitimate office of conveying the pollen to the young seed is at an end, and they are, therefore, past use for cross-breeding, but they may yield to the influence of the pollen up to the moment of the first derangement; and as we know the stigma, or very point of the pistil, is the last part of the flower to come to perfection, whatever the disturbing cause which occasions the monstrosity, it must be in operation in the juices of the parent plant long before it reaches the pistils. We know, also, that certain peculiarities in plants, as well as in animals, are transmitted to their offspring; therefore, it is obvious enough that if the influence which causes monstrosity is already in operation in the juices of the plant, but not yet so far advanced as to hinder the operation of the pollen, this influence may be transmitted to the seedlings from such a cross; hence the difficulty of procuring fine double roses from seeds. It is not necessary that the young seedlings should manifest the green eye, to prove that they inherit some inherent quality from their parents which deranges the symmetry and beauty of their flowers—it is enough if the influence appears in any other form. Now, this brings us to the question, What causes the green centres in roses? If we knew the real cause we could apply a remedy, and this, for the production of new seedlings, would be of immense advantage. To make a short story of a long one, which has already exceeded too far, I may say that over-feeding in the absence of strong sunlight is generally believed to be the cause of green centres, and that most of the maladies or other peculiar appearances in plants have originated from the culture in the previous season or seasons. If this be so, the heavy and constant rains of last summer, and consequently the absence of sun heat and light, will account for the prevalence of green centres in the rose this season. From all this, and from observations I have made on other plants. I am led to infer that the success of the French rose growers in raising so many fine seedlings is owing chiefly to the fact, that they almost always keep their breeding plants in pots, so as to have them under better control in respect to feeding. Indeed, I have no doubt at all in my own mind on the subject. Their clear atmosphere may also assist them; but the Germans have the same advantage; and the Italians, with a still clearer atmosphere, have not been able to compete with the French in this branch of gardening.