Verbena(Vervain).Verbenaceæ.
Seeds; also by cuttings of vigorous shoots. Some species by divisions.
Vernonia, including Ascaricida (Ironweed).Compositæ.
May be raised from seeds, divisions, or cuttings, depending on the character of the plant.
Veronica(Speedwell).Scrophularineæ.
Seeds and divisions. Shrubby sorts often by cuttings.
Vesicaria(Bladder-pod).Cruciferæ.
Annuals by seeds; perennials by division.
Vetch(Vicia sativa).Leguminosæ.
By seeds in open air.
Viburnum.Caprifoliaceæ.
Seeds, which should be stratified. They usually remain dormant the first year. Layers usually make the best plants. Green cuttings made in summer and handled in frames give excellent results.V. plicatumis propagated by cuttings.Ripe cuttings are sometimes used for the soft-wooded species. The snowball or guelder-rose (V. Opulus) is rapidly increased by layers. It is also a good stock for closely related species.V. LantanaandV. dentataare good stocks on which varieties difficult to handle can be worked by the veneer-graft during winter.
Victoria(Royal Water Lily, Water Platter).Nymphæaceæ.
The seeds should be kept in vessels of water until ready for sowing, when they may be placed in loamy soil, and the pot submerged a couple of inches in water, the temperature of which should not be allowed to fall below 85°. The tank should be in a light position near the glass. Annual.
Vinca(Periwinkle).Apocynaceæ.
Increased by seeds and by divisions.
Viola(Violet, Heartsease, Pansy).Violarieæ.
The named violets are increased by cuttings made in a cool house from vigorous shoots. Common species by seeds, runners and divisions of the plants. Pansies are usually grown from seeds, but named varieties may be multiplied from cuttings taken late in the season, or from layers.
Virgilia.SeeCladrastis.
Virginia Creeper.SeeAmpelopsis.
Virgin’s Bower.SeeClematis.
Viscum(Mistletoe).Loranthaceæ.
Raised from seed, which should be inserted in a notch cut in the bark or under side of a branch of the host. Avoid crushing the seed, and have the embryo directed towards the trunk. To prevent birds from disturbing the seeds after being placed in position, cover with light-colored cloth. The seed may also be fastened to a smooth part of the tree by the sticky substance surrounding it, but more seed is lost. Our native phoradendron can be handled in the same way.
Vitex(Chaste-tree).Verbenaceæ.
Seeds. Suckers. Layers. Cuttings of green or ripened wood.
Vitis.SeeGrape.
Vochysia, Curcullaria.Vochysiaceæ.
Seeds; by ripened cuttings in sand under glass, in heat.
Waahoo.SeeEuonymus.
Waldsteinia.Rosaceæ.
May be multiplied by seeds or divisions.
Wall-flower(Cheiranthus Cheiri).Cruciferæ.
Propagated by seeds; the plants, however, will not flower at the north until the second season; protection of a frame is required.
Wallichia, Wrightia.Palmæ.
May be increased by seeds; or by suckers, which should be gradually separated so as to allow them to make sufficient roots before they are quite detached.
Walnut.SeeJuglans.
Water-Cress(Nasturtium officinale).Cruciferæ.
Cuttings of the young stems, which root in mud with great readiness. Seeds scattered in the water or mud.
Water Lily.SeeNymphæa, Nelumbo and Victoria.
Water-Melon(Citrullus vulgaris).Cucurbitaceæ.
Seeds, usually sown where the plants are to remain, after the weather is warm and settled.
Watsonia(Bugle Lily).Irideæ.
The plants are multiplied by seeds or by offsets.
Wax Flower.SeeHoya.
Weigela.SeeDiervilla.
Wellingtonia.SeeSequoia.
Whin.SeeUlexandGenista.
White Cedars.SeeChamæcyparisandThuya.
White-wood.SeeLiriodendronandTilia.
Whitlava.SeePhacelia.
Whortleberry, Huckleberry (Gaylussacia resinosa).Ericaceæ.
Propagated by seeds, which should be stratified and otherwise carefully handled. (See alsoVaccinium.)
Willow.SeeSalix.
Wind Flower.SeeAnemone.
Windsor, Broad or Horn Bean(Vicia Faba.)Leguminosæ.
Propagation by seeds in open air after the soil is fairly warm.
Winter Aconite.SeeEranthis.
Winter Cress.SeeBarbarea.
Wistaria.Leguminosæ.
Readily grown from seeds. Sometimes by division. Layers. Cuttings of ripened wood, usually handled under glass. The common purple and white kinds are largely grown from root-cuttings, an inch or two long, placed in bottom heat, when they will start in four or five weeks. Many of the fancy kinds, especially when wood is scarce, are root- or crown-grafted uponW. Sinensis.
Witch-hazel.SeeHamamelis.
Woad-Waxen.SeeGenista.
Woodbine.A name properly belonging to climbing Loniceras, but often applied to Ampelopsis, both of which see.
Wormwood, Southernwood (Artemisia Absinthium).Compositæ.
Seeds and division.
Wrightia, Balfouria (Palay or Ivory-tree).Apocynaceæ.
Seeds; usually by cuttings, which root readily in sand in heat.
Xanthoceras.Sapindaceæ.
Usually multiplied by seeds; root-cuttings are sometimes used.
Xanthorhiza, Zanthorhiza.Ranunculaceæ.
Seeds and suckers.
Xanthorrhœa(Black Boy, Grass-tree).Juncaceæ.
Seeds; but usually by offsets.
Xanthosoma, including Acontias.Aroideæ.
May be increased by cutting up the stem or root-stock into small pieces and planting these in light soil, or cocoa fibre, in bottom heat. After a stem has been cut off, a number of shoots are developed, which can be treated as cuttings.
Xerophyllum.Liliaceæ.
May be propagated by seeds and by divisions.
Xiphion.SeeIris.
Xylophylla.SeePhyllanthus.
Yam.SeeDioscorea.
Yellow-wood.SeeCladrastis.
Yew.SeeTaxus.
Yucca(Adam’s Needle, Bear’s Grass, Spanish Bayonet).Liliaceæ.
Increased by seeds; and by divisions, which may be planted in the open ground, or by pieces of thick, fleshy roots, cut into lengths, and inserted in sandy soil, in heat.
Yulan.SeeMagnolia.
Zamia.Cycadaceæ.
Division of the crowns when possible; or by seeds and suckers. The plants are oftenest imported directly from the tropics.
Zanthorhiza.SeeXanthorhiza.
Zanthoxylum(Prickly Ash).Rutaceæ.
Seeds, suckers, but more often by root-cuttings.
Zea.SeeMaize.
Zephyranthes, including Habranthus (Flower of the West Wind, Zephyr Flower).Amaryllideæ.
May be multiplied by seeds; or by separating the bulbels.
Zingiber, including Zerumbet (Ginger).Scitamineæ.
Propagated by division.
Zinnia(Youth-and-old-Age).Compositæ.
Seeds, sown either in-doors or out.
Zizania(Wild or Indian Rice).Graminæ.
Seeds, sown along water courses or in bogs in fall or spring.
Zizyphus.SeeJujube.
Zygadenus, including Amianthemum, Anticloa.Liliaceæ.
Readily multiplied by seeds or by divisions.
Zygopetalum.Orchideæ.
Division. (See also underOrchids.)
Zygophyllum(Bean Caper).Zygophylleæ,.
Seeds, when they can be had; otherwise by cuttings in a frame.
CHAPTER VII.
POLLINATION
Pollination.—The act of conveying the pollen from the anther to the stigma.
Close-pollination—Self-pollination.—The transfer of pollen to a stigma of the same flower.
Cross-pollination.—The conveyance of pollen to the stigma of another flower.
Crossing.—The operation or practice of cross-pollinating.
Fertilization—Fecundation—Impregnation.—The action of the pollen upon the ovules.
Close-fertilization—Self-fertilization.—The action of pollen upon the ovules of the same flower.
Cross-fertilization.—The action of pollen upon the ovules of another flower of the same species.
Individual-fertilization.—Fertilization between flowers upon the same plant.
Hybridizing.—The operation or practice of crossing between species.
Hybridism—Hybridity.—The state, quality or condition of being a hybrid.
Hybridization.—The state or condition of being hybridized, or the process or act of hybridizing.
Cross.—An offspring of any two flowers which have been cross-fertilized.
Individual-Cross.—An offspring of two flowers on the same plant.
Cross-breed—Half-breed—Mongrel—Variety-hybrid.—A cross between varieties of the same species.
Hybrid.—An offspring of plants of different species.
Half-hybrid.—A product of a cross between a species and a variety of another species.
Derivative or Derivation-hybrid—Secondary-hybrid.—A hybrid between hybrids, or between a hybrid and one of its parents.
Bigener—Bigeneric hybrid.—A hybrid between species of different genera.
Bigeneric half-breed.—A product of a cross between varieties of species of different genera.
Mule.—A sterile (seedless) hybrid.
GENERAL REQUIREMENTS.—In order to understand the methods of pollination, the reader must be able to recognize the parts of the flower. The fuchsia,Fig. 90, shows the parts distinctly. The open flower, on the right, contains four well-marked series of organs. The first series is composed of four narrow and leaf-like parts or sepals, collectively called the calyx. Borne upon these is the corolla, made up of four blunt and variously colored petals. The next series comprises eight slender stamens or male organs (S). The thread-like portions or stalks of these are the filaments and upon them are borne the anthers. The anthers contain the pollen. The last and innermost series is a pistil or female organ (P). The pistil is made up of three parts: the ovary, which develops into the seed-pod, the style or slender portion, and the stigma, or enlargement at the end. The ovary in this case is the oblong body borne at the base of the flower and upon which the other parts stand. The style runs through the flower to the ovary.
Fig. 90. Parts of the Flower.
Fig. 90. Parts of the Flower.
The modifications of the flower are numberless, both in form and number of parts, but these four series of organs—the calyx, corolla, stamens and pistils—always comprise a complete flower and they are arranged in the order named. A perfect flower is one which contains both stamens and pistils without any reference to the surrounding or leaf-like organs. Many flowers are imperfector contain only one sex. When the sexes are borne in different flowers upon the same plant, the species is said to be monœcious; and when they are borne upon different plants the species is diœcious. Sometimes the inflorescence is mixed, some flowers being perfect, some staminate and some pistillate, all upon the same plant; such species are polygamous. Most garden plants have perfect flowers. Many nut-bearing trees are monœcious, as walnuts, butternut, hickories, chestnuts, hazels and filbert and oaks. Some of the composite plants are also monœcious, the large head bearing staminate flowers in one part and pistillate in another. Pumpkins and squashes are monœcious and so are most varieties of melons.Fig. 91shows a pistillate pumpkin flower with the ovary or young pumpkin below, andFig. 92a staminate flower which lacks the enlargement below. Among diœcious species may be mentioned the willows and poplars.
Fig. 91. Pistillate Squash flower.
Fig. 91. Pistillate Squash flower.
The ovary contains the ovules. When these are acted upon or fertilized by the pollen they develop into seeds. The pollen falls upon the stigma or upper extremity of the pistil, and each grain germinates and sends a tube down through the style to an ovule. The stigma is a slightly roughened soft surface, and when it is “ripe,” or ready to receive the pollen, it becomes slightly moist or sticky. In most plants the stigma is merelya circular expansion of tissue (Fig. 97), but sometimes it is divided into lobes and the lobes remain closed until it is ready for the pollen. The fuchsia stigma is composed of four lobes, which are closed inFig. 90.Fig. 93shows the two-lobed stigma of the trumpet-creeper or tecoma before the flower is ready for pollination.Fig. 94shows the stigma open, in condition to receive the pollen. In these flowers the stamens are hidden in the tube of the corolla.
Fig. 92. Staminate Squash flower.
Fig. 92. Staminate Squash flower.
The pollen is nearly always in the form of very small grains, which become dry when ripe. In some plants, notably in orchids, the pollen is borne in large masses known as pollinia. When the anther is “ripe” it assumes a yellow, orange or brownish cast and the pollen is discharged through a split in the side, a chink at the apex or other aperture. The pollen may fall upon and fertilize the stigma of the same flower, in which case the flower is said to be self-fertilized, or oftener it is carried to another flower by insects, winds or other agencies. Most plants possess some contrivance which renders self-fertilization difficult and cross-fertilization easy.
Fig. 93. Closed stigma of tecoma.
Fig. 93. Closed stigma of tecoma.
Fig. 94. Open stigma of tecoma.
Fig. 94. Open stigma of tecoma.
There are many degrees of cross-fertilization. The cross may take place between two flowers in the same cluster or between two clusters upon the same plant; or it may take place between distinct plants, either of the same or of another species. Fertilization between flowers on the same plant is known as individual-fertilization. The limits within which crossing is possible are not known, but the closer the species are related the more readily, as a rule, will they cross. One of the barriers which nature erects to prevent self or close-fertilizationis a difference in time of maturing of the two sexes. In any flower the two parts are rarely ready at the same time. Flowers in which the stamens mature first are said to be proterandrous, and those in which the pistils mature first are proterogynous. 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. If the pollen matures first, it is only necessary to keep it a few days until the pistil is ready; but if the pistil matures first, and the plants cannot be handled artificially, the pollen must be keptover until the following season in order to effect any crosses.
The longevity of pollen is little understood. That of some species will keep much longer than others. It is supposed that, as a rule, it will not keep beyond a few days or weeks. If the pollen is to be kept, the anthers should be picked just before ready to burst and laid upon paper in a warm, dry and shady place until they dry up and the pollen is all discharged. The anthers must then be removed, and the pollen is securely wrapped in dry paper. If it is to be kept long it will probably be better to place it in small, closely cork-stoppered vials. It should be kept in a uniform temperature.
Methods.—All perfect flowers—those which contain both stamens and pistils—must be deprived of their anthers before the pollen is discharged, to prevent self-fertilization. This removal of the anthers is calledemasculation. It is performed before the flower opens, and therefore before any foreign pollen could have reached the stigma. In some flowers, as in the tomato,Fig. 95, the stigma protrudes even before the petals are fully grown and emasculation must be performed very early. Even if the stigma is not mature, there is a chance that pollen will adhere to it and persist until conditions are fit for its growth.
The flower is generally emasculated by pulling out the anthers with pincers, but some large anthers can be hooked out easily by a very small crochet-hook or by a pin bent to a minute hook upon the point.
Fig. 95. Tomato-flower.
Fig. 95. Tomato-flower.
It is many times a tedious operation, however, to pull out the anthers without crushing them, and thus distribute some of the pollen. A surer and better plan with most flowers is to cut off the floral envelopes and the stamens near the base with a pair of small and sharp-pointed scissors which cut well at the point.AinFig. 90shows the point at which this cut should be made in the fuchsia. With a little practice, one can cut off the parts quickly.Fig. 96shows a tomato-flower afterit has been emasculated in this fashion.Fig. 97represents two flowers ofNicotiana affinis, one of which has been cut. One of the most important features of this method is the marking of the fruits which results in all species in which the calyx persists. The calyx, of course, does not develop and the crossed fruit can be distinguished at once, even though the label is lost. The tomato fruit inFig. 98lacks entirely the long leaf-like calyx lobes at the base.Fig. 99shows upon the right a gooseberry fruit, of which the flower was cut, while that on the left illustrates an untreated fruit with the long persistent calyx. This marking of the calyx is useful in all the pomaceous fruits, like apples and pears, and even in capsular fruits, like phloxes and petunias, in which the calyx lobes remain green.
Fig. 96. Emasculated tomato-flower.
Fig. 96. Emasculated tomato-flower.
Fig. 97. Nicotiana affinis.
Fig. 97. Nicotiana affinis.
As soon as the flower is emasculated it must be securely tied up with a bag, to exclude pollen, as seen inFig. 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 such cases, all the remaining flowers in the cluster should be removed and the bag should be tied over a portion of the branch. The branch will often need to be cut off to accommodate the bag. If there are many large leaves about the flowers, part of them will need to be cut off. It is always a good practice to emasculate two or three flowers in the cluster—or all those of the same age—inorder to multiply the chances of success. If flowers of different ages are emasculated, however, the bag will have to be removed several times to apply the pollen as the stigmas mature, and the chances of success will be lessened, for the flowers should be handled as little as possible.
Fig. 98. Crossed tomato.
Fig. 98. Crossed tomato.
Various bags have been devised and recommended for covering the flowers, but none of them yet introduced are equal to the ordinary grocers' manilla bags. The only difficulty is that the smallest size—the fourth-pound—is too large for many small subjects, but for these the bag can be cut off. A soft string, five or six inches long, is passed through one of the folds of the bag about an inch from the open end, as seen inFig. 101, and is tied to hold it in place. To make the bag pucker tightly about the stem, it should be moistened just before it is used.
In some flowers which have long and thick tube-like corollas, and in which the stigma matures quickly, the end of the corolla itself may be tied up. The flowers of squashes and pumpkins are particularly adapted to this treatment, and one is shown inFig. 102. The flower is tied before it opens. In squash-like plants the flowers usually open early in the morning and the flowers are tied up the preceding evening. The corollas soon wilt and bags must be used after the pollen is applied; and even if the corolla does not wilt and shrivel, insects sometimes eat through it and interfere with the experiment.
All imperfect flowers of course need no emasculation, but they must be tied up while yet in the bud to protect them from pollen.
Fig. 99. Crossed and uncrossed gooseberries.
Fig. 99. Crossed and uncrossed gooseberries.
As soon as the stigma matures—which will vary from one to six or seven days, according to the species—the pollen must beapplied. The novice will be obliged to remove the bags occasionally, to see if the stigmas are ready. As soon as the shiny or glutinous appearance of the stigma is seen, pollination should be performed. The pollen is most easily secured by removing an anther when it is about to burst and breaking it open. If the anther is allowed to break open naturally, the pollen will be lost, or at least difficult to secure. There are various instruments recommended to aid in the transfer of the pollen. A camel’s hair brush is often advised, but it is probably the poorest instrument which can be used. It wastes the pollen and also mixes it by holding it among the hairs, and it is often a difficult matter to apply pollen to the stigma evenly and in sufficient amount. The point of a small knife-blade is a better instrument. A still handier and better tool is made by flattening the point of a pin and then inserting the little scalpel in a handle, as shown inFig. 103. With the point of this implement the pollen can be removed from the groove or opening in the side of the anther. It is commonly better, however, to place the unopened anther upon the thumb nail and crush it with the scalpel, when the pollen can be gathered up on the point and transferred to the stigma. In some species the pollen can be removed only by opening the anther-valves dexterously. Such is the case with the tomato; the point of the scalpel is inserted in a longitudinal groove or fold in the side of the anther, and as it is carried upwards the pollen is secured.
Fig. 100. Flower tied up.
Fig. 100. Flower tied up.
The stigma should receive an abundant supply of pollen. No harm can come from supplying too much while if too little is applied, some of the seeds will not mature or even the fruit may not set. It is well known that in many plants, at least, thepollen stimulates the development of the fruit-walls, as well as fertilizes the ovules, and a greater amount of pollen than is sufficient to produce the seeds themselves may therefore exert an important influence. Sometimes it is not necessary to use an instrument to transfer the pollen. If the pollen is copious and adheres to the anther after it is discharged, the anther may be simply rubbed over the stigma. An anther will ordinarily contain sufficient pollen to fertilize several stigmas. The whole surface of the stigma should be covered until it is colored with the pollen. Sometimes it will be found advisable to cut off the corolla from large flowers, if it was not done when the flower was emasculated, to facilitate the labor of applying pollen. The short stigmas of squashes, for instance, can be reached more easily if the corolla is removed, as inFig. 104.
Fig. 101. Bag.
Fig. 101. Bag.
In order to prevent the mixing of pollen, the flowers from which it is to be derived should be covered while in the bud, the same as the flowers designed as the pistillate parents. Otherwise foreign pollen may be deposited upon the anthers by insects or winds.
Fig. 102. Squash flower tied up.
Fig. 102. Squash flower tied up.
As soon as the pollen is applied to the stigma, the flower should be tied up again the same as before. The bag should remain three or four days or a week, until the stigma has died and all danger ofanother pollination is removed. If the fruit is likely to be destroyed by birds or insects, it should be covered with netting bags as soon as the paper-bags are removed. These bags also serve to mark the crossed fruits, and to catch them if they should drop before the operator is aware. Of course all crosses should be labelled with the names of both parents and the date of the operation.
Fig. 103. Pin-scalpel.
Fig. 103. Pin-scalpel.
For ordinary operations, no especial outfit is necessary for the crossing of plants, but those who experiment largely will find that the work will be greatly facilitated by the use of a portable box in which the various requisites can be carried. If this box has a compartment for every article, the operator will see at a glance if anything is lacking before he goes to the field. Figs.105and106illustrate a convenient pollinating kit. This is made about 12 inches long, 9 inches wide and 3 inches deep. In the central portion is a compartment for bags and one for labels. At the right end, running crosswise, is a narrow compartment for string, and at its upper end is a small bottle of alcohol. Into this alcohol the scalpel and other tools are dipped whenever another kind of pollen is to be used, in order to destroy whatever pollen grains may adhere to them. In front is a compartment for a magnifying glass, and a long one to hold scalpel, brushes, crochet-hook and pencil. The note-book is held in the cover by a wire clasp.
Fig. 104. Treated squash flower.
Fig. 104. Treated squash flower.
It is rare that all the flowers which one pollinates will mature fruit. If one-half are successful on the average, the operator may be satisfied. External conditions have much to do with the success of the operation. Some species do not set well during very dry weather and some are impatient of confinement. But probably all plants which thrive under glass are more sure to give goodresults if pollinated under confinement, because conditions are under control.
Crossing of Flowerless Plants.—Ferns, lycopodiums, and their allies, pass through two stages of development, and fertilization takes place only in the first stage. When spores germinate, a small, thin, green tissue spreads over the soil. This tissue is the prothallus (or prothallium). Upon the prothallus, or somewhat sunken in it, the sexual organs appear. They are minute aggregations of cells. Some of these aggregations develop into sperm or male organs and some into germ or female organs. The sperm organ is known as an antheridium and the germ organ as an archegonium. Spermatozoids are formed in the antheridium, and these enter the archegonium and fertilize the germ cell. This fertilized germ cell then develops into the second stage of the species, or into that part which we know as the fern or the lycopod. During this second stage, the plant bears leaf-like organs and it also produces numerous spores. These spores will produce the prothallus again when sown. Ferns, therefore, are fertilized but once during their lifetime, and the spores are not the direct result of fertilization as are the seeds of flowering plants.
Fig. 105. Pollinating Kit, closed.
Fig. 105. Pollinating Kit, closed.
If ferns and other flowerless plants are to be crossed, therefore, the operation must be performed in the prothallic stage. It was long a matter of doubt among botanists as to whether crossing is possible among these plants, but it is now known that it does occur. It has been brought about repeatedly in cultivation. The sperm bodies are not transferred by hand, but the spores of the species between which crosses are desired are sown together and the transfer is allowed to take place naturally. The prothallia of ferns are nearly always diœcious (sexes borne on different plants), so that crossing in such cases is not improbable.Many spores should be sown to increase the chances of success, and care should be taken that the different kinds germinate simultaneously. Some species germinate quicker than others, and the operator must determine by previous trial what these differences are. (For methods of sowing spores, seepage 24.) Only a small part of the plants will be likely to be crosses. In one of Lowe’s experiments, only five plants out of 1,000 were undoubted crosses.
Fig. 106. Pollinating Kit, open.
Fig. 106. Pollinating Kit, open.
ORDINAL INDEX.
An Index to the natural orders or families mentioned in the Nursery List. A number in parentheses indicates the number of references to the family upon a page, if more than one occurs.