Wind pollination

“ When ripe the wind blows the pollen as it scatters from the dangling stamens, and some of the grains reach the stigmas of the female flowers; here they germinate, each pollen grain sending a delicate pollen-tube down the style into the ovary of the flower. This process of application of the pollen grains to the stigma is termed pollination, and depends on the wind.
The female inflorescences are also spikes (Fig. 32, A) , but they bear only one to five flowers, and stand off from the axils of the foliage leaves. ”

“ In many cases cross-pollination is assured because the stamens and the pistils are in different flowers (diclinous) . Monœcious and diœcious plants may be pollinated by wind or insects, or other agents (Fig. 204) . They are usually wind-pollinated, although willows are often, if not mostly, insect-pollinated. The Indian corn is a monœcious plant. The staminate flowers are in a terminal panicle (tassel) . The pistillate flowers are in a dense spike (ear) , inclosed in a sheath or husk. Each “silk” is a style. Each pistillate flower produces a kernel of corn. ”

“ The wild red or yellow plum forms dense thickets in moist woods and along river banks from New York to Texas and Colorado. Its leafless, gnarled, and thorny twigs are covered in spring with dense clusters of white bloom, honey-sweet in fragrance, a carnival of pleasure and profit to bees and other insects. In hot weather this nectar often ferments and sours before the blossoms fall. The abundant dry pollen is scattered by the wind. The plum crop depends more upon wind than upon insects, for the pollination period is very brief. ”

“ Flies and some other insects are agents in cross-pollination. Humming birds are also active agents in [Pg 44] some flowers. Snails are said in rare instances to carry pollen. Man and the domesticated animals undoubtedly frequently pollinate flowers by brushing past them through the fields.
Pollination by the Wind.—Not all flowers are dependent upon insects or other animals for cross-pollination. Many of the earliest of spring flowers appear almost before the insects do. Such flowers are dependent upon the wind for carrying pollen from the stamens of one flower to the pistil of another. ”

“ 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 it was possible to cause the insect to benefit the plant at the same time as it was pillaging the pollen, by carrying some of it to female blossoms and thereby securing cross-fertilization, it would be of great advantage, for the plant would no longer require to produce such enormous quantities of pollen, and the fertilization would be much more certain than when it depended on the wind. It is obvious that the successful pollination of anemophilous plants implies good weather and a favourable wind. ”

“ It is best to pull off the undeveloped male flowers if they happen to be on the same branch with the female flowers, and then place the bags over the female flowers at about the time when they blossom, in advance of pollination of the male flowers. It is not safe to depend upon pulling off the male flowers of an isolated tree and leaving the female flowers without bags to protect them from pollen of the same species or of allied species, for the reason that wind may carry pollen to a great distance. ”

“ 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. ”

“ 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. ”

“ It might with the sweet-pea, but even if it did, the pollen from the same flower is not as good as the pollen from another flower from a different plant, and the seed would be poor and the plants would grow weaker every year. There are many insects that act as servants to the flowers, and the wind is one of the servants, too. It shakes the corn-tassel so that the pollen falls on the silk and makes the ear, and it carries the pollen of one stalk to the silk of another—sometimes from one field to another. ”

“ 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. ”

“ But the meadow-rue, which produces a super-abundance of very light, dry pollen, easily blown by the wind, is often fertilized through that agent also, just as grasses, plantains, sedges, birches, oaks, pines, and all cone-bearing trees are. As might be expected, a plant which has not yet ascended the evolutionary scale high enough to economize its pollen by making insects carry it invariably overtops surrounding vegetation to take advantage of every breeze that blows. ”

“ Continued rainy, damp and cold weather at the time of blooming is apt to sour the pollen or actually wash it away and thus prevent the fertilization of the blossoms, without which a crop is impossible. Bees and other insects are the principal means of accomplishing the pollination of almonds and such weather prevents them from working. ”

“ When the male and female parts of flowers are situated on different plants, as is the case in the willow, the poplar, the melon vine, and many other species, the pollen of the male flower is wafted by the wind or gentle breeze to the stigma of the female flower, which will usually be found at no very great distance, although fertilization may take place in this way at very considerable distances. ”

“ That is enough, the pumpkin will come.
“The absolute necessity of pollen for the formation of fruit explains to us the harmful effect of violent winds and prolonged rains in blossoming time. Swept away by blasts of wind, or washed away by rains, or simply spoiled by long-continued moisture, the dust of the stamens no longer acts on the ovaries, and the flowers fall without fructifying. This ruin of the harvest from lack of pollen is known as blight.” ”

“ 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. ”

“ It is obvious that, to secure cross fertilization, there must be some agent to transfer the pollen from one plant to another. Most commonly, either the wind is taken advantage of for this purpose, as with elms, pines, grasses, etc., or else flying insects are induced to perform the office, as is the case with the majority of our familiar flowers. The wind is a very wasteful carrier, so that for every grain that is properly placed, thousands, or even millions, may be lost. ”

“ They fall on barren ground; they litter the earth miles away from their parent trees, or cover the surface of lakes for miles with a yellow film—their purpose futile and their production vain. True it is, as the botanist will tell us, that more pollen must be produced in the case of wind-fertilized plants than is found in that of insect-impregnated flowers. ”

“ On the grasses tall and heavy the purplish blue pollen, a shimmering dust, sown broadcast over the ripening meadow from July's warm hand—the bluish pollen, the lilac pollen of the grasses, a delicate mist of blue floating on the surface, has always been an especial delight to me. Finches shake it from the stalks as they rise. No day, no hour of summer, no step but brings new mazes—there is no word to express design without plan, and these designs of flower and leaf and colours of the sun cannot be reduced to set order. The eye is for ever drawn onward and finds no end. ”

“ But if for some reason it becomes easier for it to grow and be fertilized in some other way, perhaps by making abundance of light pollen which is blown by the wind, as in the maple trees, then it may gradually lose its petals, as it depends less and less on insects and more and more on the wind for cross-fertilization. Nothing in life stands still ”

“ Delpino long ago pointed out that the blossom is best adapted to pollen-collecting bees, which, alighting on the two long, protruding stamens, rub off pollen on their undersides while clinging for support to the wool on the three shorter stamens, whose anthers supply their needs. As a bee settles on another flower, the stigma is calculated to touch the pollen on his under side before he gets dusted with more; thus cross-pollination is effected. Three stamens furnish a visitor with food, two others clap pollen on him. Numerous flies assist in removing the pollen, too. ”

“ A pollen grain must fall on the hollow tip of each silk, and slide a hair root down the long tube to the egg, or there would be no kernels, or seeds, on the ear of corn.
The wind is the only messenger of the pines and palms, the grasses and grains, and many of the straight-veined plants. The lilies and other bulb plants of the straight-veined family, have bee and insect visitors. Nearly all of the net-veined plants have such sweet blossoms and fruits that bees and butterflies visit them. ”

“ Even now poplars, alders, birches, and oaks rely chiefly upon the wind to carry their pollen. These plants were amongst the first of our modern flora to appear upon the earth. Some of them possess very neat contrivances suited to the wind. The catkins of the alder, for example, hang downwards, so that each little male flower is protected from rain by a little scale or bract above it. The pollen is very light, dusty, or powdery, so as to fly a long distance. The Scotch fir (Pinus sylvestris) has male flowers in little cones. ”

“ Doubtless the aster's remote ancestors were simple green leaves around the vital organs, and depended upon the wind, as the grasses do--a most extravagant method--to transfer their pollen. Then some rudimentary flower changed its outer row of stamens into petals, which gradually took on color to attract insects and insure a more economical method of transfer. Gardeners to-day take advantage of a blossom's natural tendency to change stamens into petals when they wish to produce double flowers. ”

“ The pollen dust is fine and light, and may be carried by the wind on to the stigma, as it sometimes is in poppies, and always is in pine-trees; but this is rather a wasteful way, because the wind blows so irregularly that very much pollen is lost and never reaches the stigma. In order to save some of this loss, and to make the pollinating more certain, flowers have arranged their parts so as to make use of the help of insects. ”

“ 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." This may be accomplished by the simple agency of the wind blowing the pollen broadcast, but it is done much better by insects, which brush against the stamens, and carry grains of the pollen to the next flower they visit. ”

“ While such a thing is not the cause of prairies, or the predominantly grasslike vegetation along sand dunes, or the exclusive spruce forests of the bleak and windy north country, it unquestionably aids in maintaining the often exclusive nature of such pure associations of plants. Over thousands of square miles on our own great plains or on the steppes of Russia, both subject to violent winds, the great bulk of the vegetation is wind fertilized. It could hardly be expected that pollen, once in the grip of such a wayward and shifting thing as the wind, should not be wasted in great quantities. ”

“ Several adaptations are found to favour the dispersal of the pollen. Wind-fertilised plants are generally tall; thus in Europe, at least, the commonest representatives of the class are shrubs or trees—witness the fir-trees, yew, juniper, oak, hazel, birch. ”

“ Many plants depend upon the wind to distribute their pollen. Such species bear slight, inconspicuous flowers which not infrequently cluster together in long, pendent catkins. This was undoubtedly the first and original form of plant marriage. Though often successful, it is very wasteful and undependable. “The wind bloweth where it listeth” and loses a million grains of pollen for every one it lodges. ”