THE SECRETION OF NECTAR
The Structure of Nectaries — The Physiology of Nectar Secretion — External Factors Influencing Nectar Secretion — The Relation of Soils to the Distribution and Vigor of Honey Plants — Rainfall and Honey Production — Humidity — Temperature and Nectar Secretion — Light and the Making of Sugar — Altitude — Extra-Floral Nectaries.
The secretion of nectar is at once one of the most remarkable and baffling functions of plant-life. Foliage leaves are factories in which are made carbohydrates, or sugars and starches, foods required for the growth of plants. But in nectar secretion the plant parts with the food that it has just manufactured. The two functions are antithetical, or directly opposed to each other. While the quantity of nectar secreted by a single nectary is small, thousands of tons are yielded by flowers in a single season. It is a reasonable and logical conclusion that nectar secretion renders a valuable service of some kind to plants. But before the discovery of its use in attracting insects in the pollination of flowers, the early botanists were greatly puzzled by the problem and offered a variety of curious explanations. Pontedera, an Italian botanist, made the ovary absorb nectar for the benefit of the seed. Linnaeus was of the opinion that its significance was not yet known. It was Kolreuter who was the first to point out that the purpose of nectar was to attract insects, which were necessary for the pollination of flowers.
The older flower biologists describe the forms and positions of nectaries at great length, and a few of them, as Caspary, Behrens, and Bonnier, investigated their structure; but of the relation of soil, temperature, and rainfall to the secretion of nectar they knew little. They would have been not a little astonished to learn of the vagaries of alfalfa, white clover, buckwheat, and cotton in yielding nectar in different localities and in different seasons. Most of our information on this subject has been derived from the observations of beekeepers, and will be found recorded in the flies of the bee journals. A large amount of data has been accumulated, but the influence of the various factors is still very imperfectly understood.
THE STRUCTURE OF NECTARIES
Nectaries may be divided into floral and extra-floral; the floral occur on all the organs of the flower, as sepals, petals, stamens, and pistils; the extra-floral are found on leaves, stems, and the involucral bracts. They are rare on the calyx, but the concave sepals of basswood secrete nectar in large drops. Nectaries occur in great variety on petals, as in the columbines, buttercups, love-in-the-mist, monkshood, aconite, hellebore, and honeysuckle. Stamens frequently bear nectaries, and sometimes whole stamens are changed into nectaries. In a great many flowers nectar is secreted by a fleshy ring or disc at the top or base of the ovary, as in umbelliferous plants, the cornel, sumac, currant, apple, pear, plum, raspberry, and strawberry.
A typical nectary consists of a little spherical mass of small cells, covered with