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design, in calling your attention to this subject, is to shew the use of the pollen in the vegetable economy.
You have seen the effect of moisture upon the pollen; you will recollect that the stigma was said to be imbued with a liquid substance, and that the anther, when ripe, throws out the pollen by the spontaneous opening of its lids or valves; the pollen coming in contact with the moist stigma, each little sack of it explodes, and the oily substance which it contains being absorbed by the stigma, passes through minute pores into the germ.
In the germ are seeds formed, but these seeds require the agency of the pollen to bring them to the perfection necessary for producing their species. You see now why the stamens and pistils are so essential to the perfection of a plant. Nature does not form a beautiful flower and then leave it to perish without any provision for a future plant; but in every vegetable provides for the renewal of the same.
The real use of stamens and pistils was long a subject of dispute among philosophers, till Linnæus explained it beyond a possibility of doubt; these organs have from the most remote antiquity been considered of great importance in perfecting, the fruit. The Date Palm, which was cultivated by the an. cients, bears stamens and pistils on separate trees; the Greeks discovered that in order to have good fruit, it was necessary to plant the two kinds of trees near together, and that without this assistance the dates had no kernel, and were not good for food.
In the east, at the present day, those who cultivate palms select trees with pistillate flowers, as these alone bear fruit. When the plant is in blossom, the peasants gather branches of the wild palm trees, whose blossoms contain stamens, and strew the pollen over their cultivated trees.
Pistillate flowers are called fertile, staminate infertile flowers.
As moisture causes the pollen to explode, rains and heavy dews are sometimes injurious to plants; the farmer fears wet weather while his corn is in blossom. Nature has kindly or. dered that most flowers should either fold their petals together, or hang down their heads when the sun does not shine; thus protecting the pollen from injury.
The fertilization of the fig is said to be accomplished by in. sects. In this singular plant the fruit encloses the flower; it is at first like a hollow receptacle, lined with many flowers, seldom both stamens and pistils in the same fig. This receptacle has only a small opening at the summit. The seeds are ferti
Use of the pollen in the vegetable economy-Real use of the stamens and pistils unknown till the time of Linnæus--Cultivation of palms in the eastFlowers fold their petals in wet weather-Fertilization of the fig.
lized by certain little flies, fluttering from one fig to the other, and thus carrying the pollen from the staminate to the pistillate flowers.
Although the fertilization of plants where the stamens and pistils are on separate flowers, depends a little upon chance, the favourable chances are so numerous that it is hardly possible, in the order of nature, that a pistillate plant should remain unfertilized. The particles of the pollen are light and abundant, and the butterflies, the honey bees, and other in. sects, transport them from flower to flower.
The winds also assist in executing the designs of nature.
The pollen of the Pines and Firs, moved by winds, may be seen rising like a cloud above the forests; the particles being disseminated, fall upon the pistillate flowers, and rolling within their scaly envelopes fertilize the germs.
A curious fact is stated by an Italian writer, viz. that in places about forty miles distant, grew two palm trees, the one without stamens, the other without pistils ; neither of them bore seed for many years; but in process of time they grew 40 tall as to tower above all the objects near them. The wind thus meeting with no obstruction, wafted the pollen to the pistillate flowers, which, to the astonishment of all, began to pro. duce fruit.
The number of plants in which the pistils and stamens are on different flowers, is few compared to those which have these important organs enclosed within the same corolla ; this is the case with most of our plants and shrubs, and even with the trees of hot countries; whose leaves being always present, might impede the passage of the pollen. On the contrary the trees of cold climates have generally the stamens and pistils on separate flowers, blossoming before the leaves come forth, and in a windy season of the year. Those which blossom later, as the oak, are either peculiarly frequented by insects, or like the numerous kinds of firs, have leaves so little in the way, and pollen so excessively abundant, that it can scarcely fail of gaining access to the pistillate flower.
In all cases the pollen and stigma are in perfection at the same time, and the stamens are generally shortest in drooping flowers, and longest in erect ones; thus in both cases hanging over the stigma. “Gardeners formerly attempted to assist nature, by stripping off the infertile flowers of melons and cucumbers, considering them as unnecessary incumbrances, since
Various methods by which nature conveys pollen to the pistillate plants Facts stated by an Italian writer-Trees of hot countries have mostly statens and pistils on the same corolla- Trees of cold countries have the stamens and pistils on separate flowers-Pollen and stigma in perfection at the same time.
they would never become fruit. But finding that they then obtained no fruit at all, they soon learned the wiser practice of admitting the winds to blow, and the insects to transfer the pollen of the infertile to the fruit-bearing flowers."*
Inflorescence.--Receptacle.-Fruit.-Mirbel's classification of
fruits.- Linnæus' classification of fruits. HAVING given our particular attention to the important uses of the stamens and pistils, we shall now proceed to consider the various ways in which flowers grow upon their stalks ; this is called their inflorescence, or mode of flowering.
Inflorescence. The position of the flower may be considered under three heads.
With respect to the organs which it contains.
With respect to the flowers which are near it, or which grow on the same peduncle.
1st. The corolla with respect to the organs which it contains.
The corolla, when it is monopetalous, supports the stamens, the number of which in this case always corresponds to the number of divisions of the limb of the corolla. When the co. rolla is polypetalous, the stamens are inserted upon the calyx or upon the receptacle; their number is then usually double the number of petals; as in the pink, which has ten stamens and five petals. When inserted beneath the germ or base of the pistil, the corolla is said to be hypo-gynous (underneath the style or inferior); as in the stramonium. When it is inserted into the calyx and surrounds the germ, as in the currant, it is said to be peri-gynous (around the style, or enveloping it). When the corolla is inserted upon the germ, as in the trumpethoney-suckle, it is said to be epi-gynous (upon the germ, or superior).
2d. The corolla with respect to the branches which support it.
The disposition of flowers upon their branches is analogous to that of leaves; thus, flowers are either radical, coming from the root, or cauline, coming from the stem; they are peduncled, or sessile, solitary, scattered or opposite, alternate or axillary. Sometimes they are unilateral, growing on one side of the branch, and sometimes fixed equally upon all parts of the pe. duncle and pointing in different directions.
Inflorescence Position of the corolla considered under three heads 1st. Corolla with respect to the organs which it contains--2d. Branches which support the corolla.
3d. The corolla with respect to the flowers which surround it, or which grow on the same peduncle.
The different modes of division of the common peduncle, into lesser peduncles or supports, cause a great difference in the appearance and situation of flowers, and
under a variety of forms. The green part which comes from the stem and supports the flower, is called the peduncle;
sometimes it is call. ed the foot stalk of the flower or fruit. The divisions of the peduncle are called pedicels.
When the plant is one flowered, the flower is usually insert. ed at the end of the stem; the peduncle in that case is scarcely distinct from the stem. The most common kinds of inflorescence are as follows; Fig. 62.
1st. Whorl (Fig. 62), an assemblage of flowers surrounding the stem or its branches, constitutes a whorl or ring ; this is seen in mint and many of the labiate plants. Flowers which grow in this manner are said to be verticillate, from the Latin word verto, to turn. Leaves surrounding the stem in a simi. lar manner are said to be stellate, or like a star.
3d. Flowers which surround the corolla-Different kinds of inflorescence -Whorl.
2d. Raceme (Fig. 63, a), consists of numerous flowers on its own stalk or pedicel, and all arranged on one common peduncle, as a bunch of currants.
3d. Panicle (Fig. 63, -6), bears the flowers in a kind of loose subdivi. ded bunch or cluster, without any regular order; as in the oat. A panicle contracted into a compact, somewhat ovate form, as in the lilac, is called a thyrse or bunch; a bunch of grapes is a good example of a thyrse.
4th. Spike (Fig. 64 a), this is an assemblage of flowers arising from the sides of a common stem; the flowers are sessile or with
very short peduncles; as the grasses and the mullein. Å spike is generally erect. The lowest flow. ers usually blossom and fade before the upper ones expand. When the flowers in a spike are crowded very close, an ear is formed, as in In. dian corn.
5th. Umbel (Fig. 64, 6), several flower stalks of nearly equal length,