Elements of agricultural chemistry, in a course of lectures of the Board of Agriculture / By Sir Humphry Davy.

  • Davy, Humphry, Sir, 1778-1829.
Date:
1846
Catalogue details

Licence: Public Domain Mark

Credit: Elements of agricultural chemistry, in a course of lectures of the Board of Agriculture / By Sir Humphry Davy. Source: Wellcome Collection.

    56/318 (page 40)
    Linnsean classification is founded. The numbers of the stamens and pistils in the same flower, their arrangements, or their division in different flowers, are the circumstances which guided the Swedish philosopher, and enabled him to form a system admirably adapted to assist the memory, and render botany of easy acquisition; and which, though it does not always associate together the plants most analogous to each other in their general characters, is yet so ingeniously contrived as to denote all the analogies of their most essential parts. The pistil is the organ which contains the rudiments of the seed; but the seed is never formed as a reproductive germ, without the influence of the pollen, or dust on the anthers. This mysterious impression is necessary to the continued succession of the different vegetable tribes. It is a feature which extends the resem- blances of the different orders of beings, and establishes, on a great scale, the beautiful analogy of nature. The ancients had observed, that different date trees bore different flowers, and that those trees producing flowers which contained pistils bore no fruit, unless in the immediate vicinity of such trees as produced flowers containing stamens. This long established fact strongly impressed the mind of Malpighi, who ascertained several analogous facts with regard to other vegetables. Grew, however, was the first person who attempted to generalize upon them, and much just reasoning on the subject may be found in his works. Linnaeus gave a scientific and distinct form to that which Grew had only generally observed, and has the glory of establishing what has been called the sexual system, upon the basis of minute obser- vations and accurate experiments.* The seed, the last production of vigorous vegetation, is wonderfully diversified in form. Being of the highest importance to the resources of nature, it is defended above all other parts of the plant; by soft pulpy * Since the time of Linnseus many eminent Botanists have investigated this interesting subject. It has been ascertained that the grains of pollen detained on the viscid stigma, send out pollen tubes, which gradually penetrate the tissue of the style and descend till they reach the ovules. That they enter the ovules through apertures in their coats, and at last penetrate the neucleus where they evacuate a fluid which is believed to become the embryo. That the embryo in its very young state is supported by nourishment laid up in the tissues of the neucleus. Without this application of the pollen, seeds are never fertile. The ovaries may grow, the fruit may swell, and present, in some instances, all the external appearances of perfect fruit, but if the seeds are not fertilized, they cannot vegetate or produce a new plant. When the pollen of one species is applied to the stigma of another, fertiliza- tion does not take place, unless the species be very nearly allied; and the plant produced by such a seed is intermediate in its characters between those of its parents. It is termed a hybrid or mule. Such hybrids are rarely capable of producing fertile seeds, and when they do so they are short lived. Between varieties of the same species, and particularly cultivated varieties, the facility of obtaining hybrids is greatly increased; and they produce fertile and often constant hybrids. This power of producing permanent hybrid varieties, has been turned to excellent account by those seedsmen and agriculturists who have lately given attention to improved kinds of turnips and several other plants; and it has been amply proved that man may in this way greatly improve and fit for the peculi- arities of artificial culture the plants presented to him by nature. It is to be regretted, however, that on this important subject, experiments have too often been conducted and recorded in a way anything but accurate or scientific.