Pollination

“ Artificial pollination of the female flowers of the local forms with pollen taken from American kinds has not yet succeeded in producing a permanent hybrid, although the result in the first generation has frequently shown great promise. ”

“ The plant has, nevertheless, not yet developed submersed pollination, the pollen-grains rising to the surface, where they are caught by the stigmas of floating female flowers. It follows that the individuals rooted in the deeper water, though growing vigorously, do not mature seed, for the production of which the species has to rely on plants which, at least at low water, are rooted sufficiently near the surface to allow the flowers to rise above it. ”

“ Before leaving the pollen-sac a division takes place in the pollen-grain into a vegetative cell or cells, from which the tube is developed, and a generative cell, which ultimately divides to form the male cells (see Angiosperms and Gymnosperms) .
When the pollen-grains are ripe, the anther dehisces and the pollen is shed. In order that fertilization may be effected the pollen must be conveyed to the stigma of the pistil. This process, termed pollination (see Pollination) , Pollination. is promoted in various ways,—the whole form and structure of the flower having relation to the process. ”

“ The percentage of cases in which seeds develop in those flowers in which artificial pollination is effected in the same flower or in two flowers of the same raceme is much smaller than when cross-pollination is effected by insects, reaching, in the case of the somewhat limited experiments of the writers, only as high as 28.5 per cent. ”

“ The pollen falls from the male spikes on the ears of the same plant, but also is easily blown on surrounding spikes. In order to get the required amount of seed it is necessary in our climate to encroach as little as possible upon free pollination, aiding the self-pollination, but taking no precautions against intercrossing. It is assumed that the choice of the best ears indicates the plants which have had the best pollen-parents as well as the best pistil parents, and that selection here, as in other cases, corrects the faults of free intercrossing. ”

“ Here in most cases the pollination is done by hand.
We noticed that nature provides that most of the flowers shall be cross pollinated. This is particularly true of the flowers of the fruit trees, and for this reason it is impossible to get true varieties of fruit from seed. For example, if we plant seeds of the wine sap apple, the new trees produced from them will not produce the same kind of apple but each tree will produce something different and they will very likely all be poorer than the parent fruit. ”

“ The plants are planted in rows and the rapidly growing branches trained upon poles stuck into the soil. Three or four male plants (with staminate flowers) are grown in an acre patch to supply the necessary pollen. Some authorities state, however, that the female plants develop enough staminate flowers to effect pollination. It is extensively cultivated in England, Germany and France. Also in New England, New York, Michigan, and in fact nearly every State in the Union. ”

“ Nature has several interesting ways of bringing about pollination. In the corn, willow, and pine the pollen is picked up by the wind and carried away. Much of it is lost, but some reaches the stigmas, or receptive parts, of other corn, willow, or pine flowers. This is a very wasteful method, and all plants using it must provide much pollen.
Many plants employ a much better method. They have learned how to make insects bear their pollen. ”

“ If he is not, he must carefully study the structure of flowers, especially those of the grape, so as to be able to distinguish the different organs and to discover when the pollen and stigma are ready for the work of pollination. ”

“ In order that fertile seed may be produced it is often necessary, and usually desirable, that the pollen which reaches the stigma should not belong to the same flower, but to a different flower of the same species; cross-pollination being the rule among seed plants, self-pollination the exception. To secure{83} the former, and to avoid the latter, many highly interesting devices are found, materially affecting the structure and development of flowers. ”

“ It might be suggested that the low percentage of cases is due to a lack of fertility in the pollen of the large stamen.
12. Estimated from the number of seed pods which normally develop, the number of flowers in which pollination is not effected is very small, not reaching, in the observations of the writers, much over six per cent.
Cassia chamæcrista.
1. Right- and left-handed flowers are produced at the same time on the plant. When several plants are taken, the number of right-and left-handed flowers produced is practically the same. ”

“ In this class the stamens and style unite into a column, and at the top of the column the pollen masses are situated; these are covered by the anther-cap, and in a cavity is the stigma with its viscid surface to receive the pollen grains.
So diverse and intricate are the forms of the flowers, and especially labellums, that there is little doubt that insect aid is necessary in their natural habitats to bring about pollination. It has been proved by the operations carried out in cross-fertilisation in gardens that no class of plants can be so readily crossed under artificial conditions. ”

“ When the pistil has reached a certain stage in growth it becomes ready for fertilization. Pollination having been effected, and the pollen-grain having reached the stigma in angiosperms, or the summit of the nucellus in gymnosperms, it is detained there, and the viscid secretion from the Fertilization. glands of the stigma in the former case, or from the nucellus in the latter, induce the protrusion of the intine as a pollen-tube through the pores of the grain. ”

“ As soon as the flower is emasculated it must be securely tied up with a bag, to exclude pollen, as seen in Fig. 100. Netting of any kind is not safe in ordinary practice, for the pollen grains are small enough to pass through it. It often happens that the flower-stem is not strong enough to hold the bag, nor large enough to allow the bag to be puckered tightly about it. ”

“ In crossing such species, flowers of different ages can usually be found so that the parts can be brought together without difficulty. But when one series of organs in all the flowers of any species perish before the other series is mature, the pollen must be kept until the pistils are ready, or one sex must be forced or retarded artificially to accommodate the other. ”

“ The annuals and biennials may be increased by seeds sown in early spring, in a frame. The perennials by seeds, or by carefully made divisions. Greenhouse species should be propagated by cuttings inserted in small single pots during early spring, and placed under glass. ”

“ To have blooming plants by holidays they are propagated by seeds, sown in spring or summer in pans or pots of light, rich, sandy soil, and kept in a close frame or hand-light, where they can be shaded till germination takes place. ”

“ Propagated by seeds, which should be sown in spring. In early autumn carefully transplant to a cool shady border. Also by divisions. Where a stock of old plants exists, layer their long slender branches any time after flowering, and cover with a mixture of sand and leaf soil; they will then root freely and establish themselves in time for spring blooming. Cuttings should be “drawn” or grown in a frame until they are soft, before they are removed. ”

“ These pollen threads are very ready to drop their yellow dust and broaden into petals. And they are just as ready to turn back again. If the seeds of the finest, double garden roses are planted, they sometimes forget all their long training, and go back to the single-petaled blossom and straggling canes of the wild rose. They have to be grown from cuttings to keep them tamed.
Left alone, nature might never have made one of our double roses of the garden. She doesn't seem to care to make the flower better. All she thinks about is the seed. ”

“ Then the pollen clings to the stigma, and down it goes through its tiny tube, to the little nest of ovules, or seeds, where it mates and at once causes the seeds to become alive. Then they grow and grow until their time comes to burst forth and develop new plants themselves.
Now, it is also important that the little visitors who come for the nectar, or honey, should fly from flower to flower and not crawl, because in doing so the pollen would drop off and never reach the mother flower, who is anxiously awaiting this important substance, so that the little seeds, or babies, may begin to grow. ”

“ As in the case of the fertilization of flowers, so in that of the dispersal of seeds, there are two main ways in which the work is effected—by animals and by wind-power. I will not insult the intelligence of the reader at the present time of day by telling him that pollen is usually transferred from blossom to blossom in one or other of these two chief ways—it is carried on the heads or bodies of bees and other honey-seeking insects, or else it is wafted on the wings of the wind to the sensitive surface of a sister-flower. ”

“ If he would explain why certain flowers are not colored at all, and how it has come about that other flowers are colored, some in chromatic harmony, and others not, he must look to the flowers themselves, and to their servants the insects. Every one knows that the pollen must find its way from the anther to the stigma, else the flower, lacking impregnation, can set no seed. For many trees, and for grasses generally, the office of transporting the pollen is performed by the wind. ”

“ When the pollen is of full size, or ripe, the little box bursts open, and out the pollen flies. The growth of the plant begins here, with the pollen.
A tiny grain of pollen, falling on the top of the pistil, begins to grow. It puts out little threads like roots. These grow down the stem, or post, of the pistil into the seed case. There they find the seed germs, and when the pollen comes to them, the germs begin to grow. They grow very fast.
It is then that the pretty flowers fade. The work of the blossom is done when the pollen is ripe, and the seed germs begin to grow. ”

“ In the mean while plenty of barren flowers are produced on a distinct root, on short straight stalks, from which they rise like little separate white bubbles, suddenly expanding when they reach the surface, and floating about in such abundance as to cover it entirely. Thus their pollen is scattered over the stigmas of the first-mentioned blossoms, whose stalks soon afterwards resume their spiral figure, and the fruit comes to maturity at the bottom of the water. ”

“ And to the question why these bright petals, whose colour and variety of form lend such charm to the world of flowers, have been developed at all, most botanists will give a prompt and very interesting reply. As both male and female elements are usually in one flower, it may fertilise itself, the pollen falling directly on the pistil. But fertilisation is more sure and effective if the pollen comes from a different individual—if there is "cross fertilisation." ”

“ In all the carices the flowers are loosely arranged in compact spikes and spikelets, with their mobile stamens hanging out freely to the breeze, and their feathery stigmas prepared to catch the slightest grain of pollen which may happen to be wafted their way by any passing breath of air. The varieties in their arrangement, however, are almost as infinite among the different species as those of the grasses themselves; sometimes the male and female flowers are produced on separate plants; sometimes they grow in separate spikes on the same plant ”

“ On other trees the catkins are greenish, and they stay on after reaching full size. They are the fertile flowers, which develop into seed pods. Pollen brought to them by the wind or by visiting insects in search of nectar, insures the setting of seed in these flowers. Though the gayer flowers fall, they are quite as necessary to the making of seeds as the fertile ones. In all the willows and poplars, it requires two trees, bearing the two kind of flowers, to make the seed. And the wind and nectar-seeking insects are necessary as pollen-carriers. ”

“ At age seven or eight the foundation for sex-instruction should be laid by information concerning plant production; that the pollen dust of the father plant becomes attached to the legs of the honey-seeking bee and is transferred to the mother plant, where it fertilizes the seed from which a baby plant grows. The function of the wind, also, in effecting the conjunction of pollen with the ovule of the stigma should be explained; and how the pollen or male principle fertilizes and gives life to the female ovule, making seed from which a new plant is born. ”

“ In species where the pollen is wind-borne as in most of our trees—firs, oaks, beech, ash, elm, etc., and many herbaceous plants, the flowers are as a rule small and inconspicuous, greenish, and without either scent or honey. Moreover, they generally flower early, so that the pollen may not be intercepted by the leaves, but may have a better chance of reaching another flower. And they produce an immense quantity of pollen, as otherwise there would be little chance that any would reach the female flower. Every one must have noticed the clouds of pollen produced by [Pg 123] the Scotch Fir. ”

“ Another way is to collect branches carrying male flowers before the flowers have developed, place them in the ice house or in a dark, cold room without light until the proper time for forcing the flowers, and if these branches are then placed in water, the water changed frequently as when we are keeping flowers carefully, the catkins or other male flowers will develop pollen satisfactorily a long time after their natural time of furnishing pollen, when they are brought out into the light. ”