This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Before alluding to the Ovule, it will perhaps be better for me to give a few brief words on the stamens and pistils, essential to all plants for the production of fruit. Stamens are the male organs of the plant, and consist of a bundle of spiral vessels surrounded by cellular tissue, termed the filament, at the top of which will be found the anthers, that finally open and discharge their contents - pollen - which is usually a powdery matter, and by whose action on the stigma the fertilisation of the ovules is accomplished. A familiar example of pollen will be found in the common garden Crocus. Let the reader take a stamen from the flower of this plant and gently rub it between the finger and thumb, and he will find both covered with pollen-grains; thus it will be easy to account for the short crops of fruit sometimes taking place. Last year, for example, the continuous rains probably washed away the greater part of these small grains, and thus prevented their being fertilised with the pistil, without which the natural consequence is, short crop.
Pistils - the female organs - are always in perfection simultaneously with the male parts (stamens): they (the pistils) are composed usually of the stigma - the parts at or near the point - to which the pollen must be applied to fertilise the seed; the style, usually very long, but sometimes absent, supporting the stigma; and the ovarium, or embryo seed-vessel. The stigma is invariably viscid or clammy,. so that immediately the pollen bursts from the anthers it adheres to it. In the saffron of shops will be recognised the stamens of a Crocus (Crocus sativus); and no wonder it is so expensive, considering that only three stamens are found in one flower, taking, as a matter of course, a goodly number to make a pound in weight. In some cases the male and female organs are in separate flowers, the fertilisation of which is often performed by insects, etc.; and it is on the number of both stamens and pistils that the great Linnaeus based his system of botany - now, however, in disuse, the natural system being much preferred by modern botanists. I shall probably say a few words about both systems in a future number. The Ovule is the rudiment of a future seed, and is inserted in the lower portion of the carpel, which is popularly known as the ovary.
A familiar and easily obtained example can be found by carefully making a vertical section of a carpel of the common Buttercup, each carpel containing one ovule. In coniferous and cycadaceous plants, the ovule is exposed and naked to the influence of the pollen. It (the ovule) is regarded by many botanists in most cases as a marginal bud, being borne upon the margins of carpellary leaves, - bringing us to the conclusion that the inner angle of each carpel, upon which the seeds are arranged, answers to the line of union of its unfolded edges. This line is called the ventral suture. "If you split a Pea carefully," says Prof. Oliver, "opening up the edge bearing the seeds, you will find, when laid open, that half of the seeds are on one edge, half on the other, each margin being alternately seed-bearing." Up the middle of the open carpel you have a strong line or nerve (the outer angle when the carpel was closed;, which is simply the midrib of the carpellary leaf, answering to the midrib which we find in foliage plants. This line is called the dorsal suture. In shape and mode of insertion ovules are somewhat numerous, and very interesting.
When it is curved downwards so as to approach the placenta (the part on which the ovule originates), it is camptotropal; when curved and grown to the lower half, anatropal; when attached by its middle, so that the foramen (the aperture through the integuments, to allow the passage of the pollen-tubes to the central part of the ovule in which the embryo is contained) is at one end and the base at the other, it is campylotropal; when the shape of a horse-shoe, it is bycotropal. There are a few other shapes, which it is not necessary to explain here.
W. Roberts. (To be continued).