Journal of Horticulture pp. 329-330 (Jan 21, 1862)
THE PROCESS OF FERTILISATION
|*CybeRose note: This should be Sinningia guttata.|
SINNINGIA, and not Limmingia (as printed at page 310), was the broken-down family which was the cause and precursor of the present race of Gloxinias. At that time there were only two kinds of Gloxinias in cultivation—the then recently-introduced Gloxinia speciosa, and the oldest of them all, the Gloxinia maculata. Both would seed very freely, each by its own pollen, but neither would unite by the pollen of the other. Both were favourites with gardeners who felt a family-like loss at their want of reciprocity; when one of them, the said gardeners, stepped out of the ranks and turned a rank radical, turned also the genus Sinningia through Sinningia maculata* to a botanical figment, united it by its pollen with the newer Gloxinia speciosa which produced glauca or glaucescens, the parent of the present race of garden Gloxinias. It may be stated as an historical fact, that the raiser of glaucescens thought so little of it that he turned out some scores of "roots" of it with the garden rubbish, the rubbish was trampled by cattle, and most of the Gloxinia bulbs were thus destroyed. One plant was kept to prove the cross. Mr. Low, sen., of the firm from Clapton, saw that plant, and picked out some "roots" from the cattle track, sold the first three of them to Messrs. Glenny and Harris, and to Mrs. Lawrence, for 21s. each. Just think of that when you have a cross seedling which may not be worth picking up on the street; if it is not a barren one never mind its present looks, give up a florist's notion at once, and call it the progenitor of some prodigious good thing, and the very daring will help to bring your prospects to good account.
Before the first crossed Fuchsia was in the market, in 1836, it was clearly proved, and agreed upon by all practicals who had seen the proofs, that the Mexican species gracilis, virgata, conica, elegans, globosa, and macrostemon, were all convertible, the one for the other, as the merest varieties of garden seedlings—say Asters or Poppies. And not only so, but that excorticata of New Zealand, and discolor of Port Famine, with the wood of which Mr. Darwin had to cook his own meals when on that station, could be produced by the mixtures of Mexican kinds. Even the most dissimilar kind in the family, the Fuchsia arborescens, crossed with some one of the Mexican fry, and produced a weeping Fuchsia, which trailed on the ground like a Strawberry, as I can vouch for, as it appeared among my own seedlings. Two very good chances of two new races had been let slip in Fuchsia.
An entire new race of Fuchsias might yet be had, to bloom exactly as does the common Laurustinus [Viburnum tinus]. The second would be less easily obtained, and the primitive moves for finding it are now too far from my mark. Fuchsia fulgens and corymbiflora never well agreed in crossing the species of former days, the foliage was too coarse, and could not be subdued—at least so it was said; but perseverance never tried to prove the question, and if we lost aught by that means, just put it down in the book against the florists' account. One thing the long Fuchsias had done, but ten to one if ever you heard of it to this day—it made dissenters of one-half of the gardeners who knew it, and of every one of the practical crossers. I say practical crossers, for at that time we had many fancy men in the line of crossing; that was a fancy which could do any fancy thing without doing it at all. What they dissented about was the way some botanists said the pollen grains found their way into the heart of the seed-pods, and to all or so many of the yet unfertilised seeds in embryo.
It has been said by learned men, and men more learned believe the thing to this hour, that the pollen has the power to separate itself into minute grains when it is sticking fast as in a pitch-plaster, on the summit of a viscous, or clammy, or sticky stigma, and that these minute grains of pollen go through very small tubes in the style as bullets go into Minnie rifles, or sink down by their own weight through the said tubes, as one might say. From the bottom of the style in flowers, there is a bridge across to the seeds, which they call the placenta, or plain bridge as one might say. How the pollen grains got over the bridge, or got along it, no one could ever tell; but some one certainly said he saw with a glass the pollen grain going down to the end of the bridge, and if he had paid the toll he might just as likely have seen the grain of pollen pass along the bridge and stop at the door of the seed itself till it was admitted. All the men who were practically engaged on crossing found a great difficulty in believing this story. They put the question thus—Do you suppose that by a beat to the tails of a miller's coat which blew the dust on to the side of a tar barrel fresh from the filling, the nearest thing we can think of to liken to the dust of the pollen on to the point of the style, would give the property to the dust to separate itself into distinct grains like small shot in a pouch or belt?
Another version of this wonder was, that each grain of pollen, as it stuck in the clammy juice on the stigma, had the power of forming a tube which reached from the stigma to the ovary, and so impregnated the seeds. In that case the late Mr. Shepherd, of the Liverpool Botanic Garden, had a bulb called Hymenocallis pedalis, in which the style was a foot long, and it had been mentioned as a case of extreme probability that a body so small as a grain of pollen could, from its own bulk, produce a tube of so much length; but that bulb was little known at the time to gardeners, though it had been figured indifferently in the nineteenth volume of the "Botanical Register," plate 1641. It was not till the long-tubed Fuchsias were in cultivation that gardeners, who were acquainted with crossing, could see the full force of the difficulty which attended those explanations of the means by which the virtue of the pollen reached the ovules. Then, although they could not gainsay it, they would not assent to it; and the sum of their objections was thus expressed—that in all the wonderful contrivances of Almighty wisdom to effect apparently difficult purposes, they had perceived that no unnecessary complication of machinery was used.
The question how the influence of the pollen reaches the ovary is yet in that same position, save and except that most gardeners believe in the mode I once explained in these pages—a mere guess, however—that the pollen grains burst on coming in contact with the gummy fluid on the stigma, and that the contents of the pollen grains, like melted sugar in water, get into the circulation like the rest of the juices of a plant; and seeing that every product of a plant depended on some part or other of the circulation of that plant—the last produced, the vitality of the seed must also depend on a part of the circulation. But whether any of these theories of the way seeds are fertilised be the correct one, no one as far as I know can tell. The probability is, that each party is well satisfied with their own way of explaining the subject, and glad enough to hold aloof from a very difficult problem.
Rare bulbs being so scarce and so little known to the public, it would be of small practical value to enumerate all that is known about their capacity for crossing. Not at present at all events. But there is one more subject connected with crossing which has not yet had the advantage of a public discussion. There are more stages than one in the process of fertilisation, though, hitherto, the work has been spoken of and written about as if the whole process consisted of one event. But the seed-pod is, as it were, the first part to take its own share of the process of crossing. You may fertilise a seed-pod so to speak, and not have a single seed in it, nor the appearance of one; and yet without the crossing, or, at least, the application of pollen, that pod would never have gone on to maturity, but fall off with the falling of the flower. In the second stage of fertilisation you only quicken the lobes or substance of the seed. If it were a Pea it was made for the pot only—there was no quickening of the germ within it. The different sections of Hibiscus, and of Cactus, and some others, are well-known instances to hybridisers of this-far-and-no-farther quickening when members of the sections are approached by pollen.
These two stages in the fertilising process are quite common. I told you not long since how I saved 10s. clear from a knowledge of that fact. I would not pay down for two seeds of Mangles' Variegated Geranium till I had ascertained if the process of fertilising them was complete or not, and, as it happened, the two first stages of the process had been reached, but that is very rare indeed in the Geranium order, as far as I have had dealings with the members. I have only one more such instance among Geraniums which I can call to mind, and how it happened throws a glimmer on the art of the cross-breeder. I well recollect having had a fine seedling open its first flowers late in October, and although it is foolish work to cross the first flowers of a very young seedling in June, or, say in the best of weather, I could not keep down the ruling passion. I ripened several pods from that cross, but none of the seeds had the germ of life quickened or fertilised, and, of course, they did not sprout.
The old Alströmeria pelegrina will ripen its seed-pod, and some few apparently ripened seeds if you touch it with the pollen of any of its nearest allies; but you, or at least I, could never get a crossed seed from that Alströmeria to sprout. Hookeriana is the next nearest to doing the same; but I believe the whole genus will give more or less evidence of the fact that full fertilisation consists of more than one process of nature. Then what you read in books about the pod beginning to swell at such and such a time after the pollen takes effect is only one of those fictions which are founded on facts; the case is as is said generally, but not always.
The lesson to learn from the fact that pods and seeds do swell and ripen sometimes without the germ having been fertilised is this—that you should apply the pollen in such doubtful cases four or five times the same day; for there never was such a thing as a stigma getting fit a second time, or after a day's interval. But as we know to a certainty that there are three if not four degrees in the quickening process, we may be excused for supposing that more pollen and most pollen will push the degrees farther and farthest if we apply it in time— that is, ere the first and final moisture on the stigma is dried up; and those which never show the moisture are more safe, one would think, if all the pollen it needs has been collected on the same day, or at the farthest on the morrow.
|*Reportedly a sport of Pelargonium
Fothergillii or P. heterogamum
But, to go still closer to the practice. When you see a chance like this, what do you suppose would have been the result if Mr. Smith, of York, had applied the pollen of the Golden Chain on Mangles' Variegated* at eight o'clock in the morning, again about eleven in the forenoon of that day, again after he had his dinner—say two o'clock, and last of all just before he went in to tea? Just think this over in your own mind. Perhaps it was the very bait for the hook to catch some one to our ways of crossing without being cross ourselves. Everybody likes flowers, but none half so much as those who pry into the secrets of nature about their origin and the ways to improve them.
This, the successive stages by which the impregnation of seeds and seed-pods is effected in some plants, has been prominently brought to my recollection by a pamphlet for which I am indebted to the kindness of Mr. Darwin. It is from the "Journal of the Proceedings of the Linnaean Society for 1862," and treats "on the two forms, or dimorphic condition in the species of Primula, and on their remarkable sexual relations." A course of interesting experiments by Mr. Darwin on the "pin-eyed" and "thrum-eyed" kinds of Primulas, and how the reversed position of the style and stamens in these flowers affects the number or the quantity of seeds which they produce.
Referring to Cowslips and Primroses, Mr. Darwin found that "the two forms exist in the wild state in about equal numbers;" also "that the existence of the two forms is very general, if not universal, in the genus Primula." In every case which he tried he found that the "pin-eyed," or long-styled plants, produced a less number, or quantity, of seeds than the "thrum-eyed," or short-style ones. Mr. Darwin thinks "the cause of this difference is, that when the corolla of the long-styled plants falls off, the shorter stamens near the bottom of the tube are necessarily dragged over the stigma, and leave pollen on it; ..... whereas, in the short-styled flowers, the stamens are seated at the mouth of the corolla, and in falling off do not brush over the lowly-seated stigma."
This is just the opinion I have been advocating, the less pollen the fewer seeds, or the still fewer number of the stages of fertilisation. Here, then, is where practice and science are brought face to face on equal grounds. The deductions which Mr. Darwin draws from this subject are, like others of his reasoning powers, most profound, and very interesting; but I must here refer the reader to the "Proceedings of the Linnaean Society" aforesaid, and ask the question, Would not the repeated application of the pollen, as above, have the effect of making up the deficiencies in all the cases mentioned both by Mr. Darwin and by Gaertner? — D. Beaton.
See Darwin on pollinating papilionaceous flowers