A Short Address on the Cross-Fertilisation
of the Viola.
GIVEN AT THE OPENING MEETING OF THE MANCHESTER BRANCH OF THE NATIONAL VIOLA AND PANSY SOCIETY,
BY MR. HENRY MARRISON
MARPLE BRIDGE, DERBYSHIRE
The best methods of growing and showing the viola have been so exhaustively dealt with that it has occurred to me it may be of interest to some of the members of the Society if, instead of attempting to add anything thereto, I speak on another branch of the subject entirely. My intention is to say a few words on the raising of new varieties by cross-fertilisation.
The subject is interesting in itself. There is further a rather pleasant thought lying behind it. It is this: he who produces a flower that, but for his efforts, would not have existed has added to the sum total of the world's beauty. In a very minute degree, it is true - still, it is there.
What I have to say will be put as plainly as possible, avoiding all technical terms except where necessity compels. I shall start with the assumption that you know nothing whatever of the subject; that you have never examined the structure of a viola flower; that you know nothing as to Nature's method of effecting pollination; and that the subject of hand cross fertilisation is to you a mystery. Please take up one of the viola blooms from the table and examine it. You will notice that it is a five-petalled flower, and further that it is bi-sexual - that is that the male and female organs of generation are on the same flower head. If you will turn the flower round and examine the back, you will at once be struck with the peculiar shape of the bottom petal. You will observe that it is drawn out, so to speak, into the shape of a spur. Now, that spur is hollow, and is really an elongated bag, which contains the nectar which is so great an attraction to our interesting little friend the humblebee. Turning the flower round again and examining the front, you will find, right in the centre where the five petals meet, a kind of knob. If you will strip off the petals, this knob stands out as a diminutive club with a small fissure or cleft near the top. There you have the stigma - an essential part of the seed bearing or female portion of the flower. Immediately behind it lies the ovary itself, closely embraced by the anthers carrying the pollen. These anthers constitute an essential part of the male portion of the flower.
Now the first thing a viola flower does on opening out really flat is to slightly spring away the five anthers from the centre of the flower. It is just sufficient to shed the pollen. If you carefully examine a flower at this stage you will find the pollen has been caught by a curious hair-like arrangement on the bottom petal of the flower. Examine a bottom petal and you will generally find some pollen right up in the throat of the flower. This is not always so; the modern exhibition viola has been so crossed and inter-crossed, with a view to increasing its size and so forth, that some few of them refuse to produce so much as a grain of pollen. This pollen-shedding, of which I have spoken, is quite automatic: the visit of the bee has nothing whatever to do with it. It is really Nature's method of preventing self-pollination; at the time the pollen is shed the female portion of that flower is not in a receptive condition. That comes later on. Now, in my opinion the bee - the ordinary humblebee - is the only insect that fertilises the viola. Other winged insects alight upon it from time to time, but they apparently make no attempt to fertilise the flower. I doubt whether they could if they wished to do so, not possessing the necessary tackle for the job. What really happens is this: the bee alights on a flower, pushes his proboscis right through its centre into the nectar pouch and sips out the nectar. In so doing he collects upon the thickened part of his proboscis the pollen that has been collected by the short hairs. Flying away to another viola he repeats the performance, and from that to another, and so on. If on this round of visits he comes upon a flower that has been open for a suitable time - which depends on the brightness of the weather - he will find the stigma in a sticky or receptive condition. Thrusting in his proboscis as before, he dusts upon the stigma some portion of the pollen he has gathered from some other flower. If that stigma is really receptive, that pollen sticks, fertilises the flower, and a seed capsule is the inevitable result.
The whole thing is a beautiful illustration of the interdependence of animal and vegetable life. Nothing in Nature stands alone. Every living organism is somewhere, in some measure, linked up to some other living thing.
Now, in cross-fertilisation by hand, you have to be the bee. For proboscis you will need a fine camel-hair brush. Trim it to a point with a sharp pair of scissors. Strip off the bottom petal of the flower from which you wish to take the pollen, and running the point of your brush through the hairs at the top of the petal, collect all the pollen you can on the tip of the brush. Turning your attention now to the flower you have selected as the seed parent, you gently dust some of the pollen grains from your brush into the cleft near the top of the stigma. It is well to examine the flower through a magnifying glass before this is done, to make sure that it is in the proper condition for pollination. If it is, a viscid or sticky spot will be noticed near the top of the stigma. It is on that that the pollen should be deposited. The whole thing is very simple, except that a little experience is needed as to the right moment to effect pollination.
The bees must, of course, be kept off the flower, or the whole operation will be useless. A good way of doing this is to cover the entire plant with a wire gauze dish-cover - it looks a bit odd in the garden, but is very effective. Or you may tie up the flower in a small muslin bag.
I find it useful to tie a piece of red wool to the flower stem after pollination, to act as a danger signal during the time the seed is ripening. Otherwise you may pick off a valuable seed pod through inadvertence.
Always select as your seed-bearing parent a plant of good habit and sound constitution. You may take pollen from a plant of indifferent habit if there is something in the flower you specially like, but never take seed from such a plant. If my experience in plant-breeding has taught me anything, it is this: that form and constitution most often follow the mother plant - the seed-bearing - whilst colour seems to follow either sex indifferently.
One little word of caution. Pollen retains its vitality quite a long time. It is therefore advisable to sterilise your brush after using it. This is done by dipping it in alcohol. Ordinary whisky will be found sufficiently deadly for the purpose.
The seed should be gathered just before it is ripe. It will ripen on the stalk after cutting. If left too long, you will probably find the empty seed capsule on the flower stalk. I always gather stalk and all, putting each cross into a separate envelope, with its parentage written on the outside.
The seed may be sown as soon as gathered and ripened - say, towards the end of July - in any good soil that has been lightened with sand. It may be sown either in the open ground or in boxes. I prefer the latter.
As soon as the seedlings have two or three rough leaves, transplant them into a cold frame and winter them there. They may, of course, be planted out in the open ground in the autumn, if the situation is favourable; but you are almost certain to lose some during the winter. In the frame, the plants are under your constant personal supervision, and the losses are very few.
The lights should be taken off the frame whenever the weather permits. By early March the seedlings will be nice sturdy plants. Harden them off and bed out.
Can we foretell the result of any particular cross? No! We cannot; the results are often truly astonishing. Amongst your seedlings you will find flowers rayed and rayless, edged and marbled, selfs and stripes. Atavism is strong in the viola. I know of no plant that breeds back to the same degree; probably because the plant itself is a hybrid. Some morning you are sure to see, peeping up arnongst your seedlings, a cat-faced looking flower, with viola-tricolour written all over its face. The original progenitor breaking through.
Can we not therefore exercise any control? Certainly we can; we can choose suitable parents. We are then sure to get some good flowers, and there is always the possibility of something extra good turning up.
In any case, you will find the whole subject - the wonderful structure of the plant, the methods adopted by Nature for its perpetuation, and also for its variation - fascinating to a degree. Familiarity here breeds neither contempt nor indifference, but, on the contrary, increasing interest. Really our happiness is very much measured by our capacity for extracting pleasure from the simple things of life. In that sense it is indeed true that, though we may never own a yard of land, the earth may be ours and the fullness thereof.
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