Agriculture for Beginners, Daniel Harvey Hill [best ereader under 100 .txt] 📗
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EXERCISE
Examine several flowers and identify the parts named in the last section. Try in the proper season to find the pollen on the maple, willow, alder, and pine, and on wheat, cotton, and the morning-glory.
How fast does the ovary of the apple blossom enlarge? Measure one and watch it closely from day to day. Can you find any plants that have their stamens and ovaries on separate individuals?
SECTION XV. POLLINATIONNature 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. In plants of this type the parts of the blossom are so shaped and so placed as to deposit pollen from the stamen on the insect and to receive pollen from the insect on the stigmas.
When you see the clumsy bumblebee clambering over and pushing his way into a clover blossom, you may be sure that he is getting well dusted with pollen and that the next blossom which he visits will secure a full share on its stigmas.
When flowers fit themselves to be pollinated by insects they can no longer use the wind and are helpless if insects do not visit them. They therefore cunningly plan two ways to invite the visits of insects. First, they provide a sweet nectar as a repast for the insect visitor. The nectar is a sugary solution found in the bottom of the flower and is used by the visitor as food or to make honey. Second, flowers advertise to let each insect know that they have something for it. The advertising is done either by showy colors or by perfume. Insects have wonderful powers of smell. When you see showy flowers or smell fragrant ones, you will know that such flowers are advertising the presence either of nectar or of pollen (to make beebread) and that such flowers depend on insects for pollination.
Fig. 36. Bees carrying Pollen
A season of heavy, cold rains during blossoming-time may often injure the fruit crop by preventing insects from carrying pollen from flower to flower. You now also understand why plants often fail to produce seeds indoors. Since they are shut in, they cannot receive proper insect visits. Plants such as tomatoes or other garden fruits dependent upon insect pollination must, if raised in the greenhouse where insects cannot visit them, be pollinated by hand.
EXERCISE
Exclude insect visitors from some flower or flower cluster, for example, clover, by covering with a paper bag, and see whether the flower can produce seeds that are capable of growing. Compare as to number and vitality the seeds of such a flower with those of an uncovered flower. Observe insects closely. Do you ever find pollen on them? What kinds of insects visit the clover? the cowpea? the sourwood? the flax? Is wheat pollinated by insects or by the wind or by some other means? Do bees fly in rainy weather? How will a long rainy season at blossoming-time affect the apple crop? Why? Should bees be kept in an orchard? Why?
SECTION XVI. CROSSES, HYBRIDS, AND CROSS-POLLINATIONIn our study of flowers and their pollination we have seen that the seed is usually the descendant of two parents, or at least of two organs—one the ovary, producing the seed; the other the pollen, which is necessary to fertilize the ovary.
It happens that sometimes the pollen of one blossom fertilizes the ovary of its own flower, but more often the pollen from one plant fertilizes the ovary of another plant. This latter method is called cross-pollination. As a rule cross-pollination makes seed that will produce a better plant than simple pollination would. Cross-pollination by hand is often used by plant-breeders when, for purposes of seed-selection, a specially strong plant is desired. The steps in hand pollination are as follows: (1) remove the anthers before they open, to prevent them from pollinating the stigma (the steps in this process are illustrated in Figs. 37, 38-39); (2) cover the flower thus treated with a paper bag to prevent stray pollen from getting on it (see Fig. 40); (3) when the ovary is sufficiently developed, carry pollen to the stigma by hand from the anthers of another plant which you have selected to furnish it, and rebag to keep out any stray pollen which might accidentally get in; (4) collect the seeds when they are mature and label them properly.
Hand pollination has this advantage—you know both parents of your seed. If pollination occur naturally you know the maternal but have no means of judging the paternal parent. You can readily see, therefore, how hand pollination enables you to secure seed derived from two well-behaved parents.
Fig. 37.
The bud on right at top is in proper condition for removal of anthers;
the anthers have been removed from the buds below
Sometimes we can breed one kind of plant on another. The result of such cross-breeding is known as a hybrid. In the animal kingdom the mule is a common example of this cross-breeding. Plant hybrids were formerly called mules also, but this suggestive term is almost out of use.
It is only when plants of two distinct kinds are crossed that the result is called a hybrid; for example, a blackjack oak on a white oak, an apple on a pear. If the parent plants are closely related, for example, two kinds of apples, the resulting plant is known simply as a cross.
Hybrids and crosses are valuable in that they usually differ from both parents and yet combine some qualities of each.
Fig. 38. Orange Blossom prepared for crossing
First, bud; second, anthers unremoved; third, anthers removed
Fig. 39. Tomato Blossom ready to cross
First, bud; second, anthers unremoved; third, anthers removed
Fig. 40.
First, blossom bagged to keep out stray pollen; second, fruit bagged for protection
They often leave off some of the qualities of the parent plants and at other times have such qualities more markedly than did their parents. Thus they often produce an interesting new kind of plant. Sometimes we are able by hybridization to combine in one plant the good qualities of two other plants and thus make a great advance in agriculture. The new forms brought about by hybridization may be fixed, or made permanent, by such selection as is mentioned in Section XVIII. Hybridization is of great aid in originating new plants.
It often happens that a plant will be more fruitful when pollinated by one variety than by some other variety. This is well illustrated in Fig. 41. A fruit-grower or farmer should know much about these subjects before selecting varieties for his orchard, vineyard, etc.
EXERCISE
With the help of your teacher try to cross some plants. Such an experiment will take time, but will be most interesting. You must remember that many crosses must be attempted in order to gain success with even a few.
SECTION XVII. PROPAGATION BY BUDSIt is the business of the farmer to make plants grow, or, as it is generally called, to propagate plants. This he does in one of two ways: by buds (that is, by small pieces cut from parent plants), or by seeds. The chief aim in both methods should be to secure in the most convenient manner the best-paying plants.
Many plants are most easily and quickly propagated by buds; for example, the grape, red raspberry, fig, and many others that we cultivate for the flower only, such as the carnation, geranium, rose, and begonia.
Fig. 41. Brighton pollinated by 1, Salem; 2, Creveling; 3, Lindley; 4, Brighton; 5, Self-pollinated; 6, Nectar; 7, Jefferson; 8, Niagara
Fig. 42. Geranium Cutting
Dotted line shows
depth to which cutting
should be planted
In growing plants from cuttings, a piece is taken from the kind of plant that one wishes to grow. The greatest care must be exercised in order to get a healthy cutting. If we take a cutting from a poor plant, what can we expect but to grow a poor plant like the one from which our cutting was taken? On the other hand, if a fine, strong, vigorous, fruitful plant be selected, we shall expect to grow just such a fine, healthy, fruitful plant.
We expect the cutting to make exactly the same variety of plant as the parent stock. We must therefore decide on the variety of berry, grape, fig, carnation, or rose that we wish to propagate, and then look for the strongest and most promising plants of this variety within our reach. The utmost care will not produce a fine plant if we start from poor stock.
What qualities are most desirable in a plant from which cuttings are to be taken? First, it should be productive, hardy, and suited to your climate and your needs; second, it should be healthy. Do not take cuttings from a diseased plant, since the cutting may carry the disease.
Fig. 43. Grape Cutting
Showing depth to
which cutting should
be planted
Cuttings may be taken from various parts of the plant, sometimes even from parts of the leaf, as in the begonia (Fig. 46). More often, however, they are drawn from parts of the stem (Figs. 43-45). As to the age of the twig from which the cutting is to be taken, Professor Bailey says: "For most plants the proper age or maturity of wood for the making of cuttings may be determined by giving the twig a quick bend; if it snaps and hangs by the bark, it is in proper condition. If it bends without breaking, it is too young and soft or too old. If it splinters, it is too old and woody." Some plants, as the geranium (Fig. 42), succeed best if the cuttings from which they are grown are taken from soft, young parts of the plant; others, for example, the grape or rose, do better when the cutting is made from more mature wood.
Fig. 44. Carnation Cutting
Cuttings may vary in size and may include one or more buds. After a hardy, vigorous cutting is made, insert it about one half or one third of its length in soil. A soil free from organic matter is much the best, since in such soil the cuttings are much less liable to disease. A fine, clean sand is commonly used by professional gardeners. When cuttings have rooted well—this may require a month or more—they may be transplanted to larger pots.
Sometimes, instead of cutting off a piece and rooting it, portions of branches are made to root before they are separated from the parent plant. This method is often followed, and is known as layering. It is a simple process. Just bend the tip of a bough down and bury it in the earth (see Fig. 47). The black raspberry forms layers naturally, but gardeners often aid it by burying the over-hanging tips in the earth, so that more tips may easily take root. Strawberries develop runners that root themselves in a similar fashion.
Fig. 45. Rose Cutting
Grafts and buds are really cuttings which, instead of being buried in sand to produce roots of their own, are set on the roots of other plants.
Grafting and budding are practiced when these methods are
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