Mendel's Law

a law of hybrids. It is named from its discoverer, Johann Mendel, an Austrian monk, Abbot of Brunn, who lived 1822-1884. He carried on experiments in cross-pollenation of peas in the garden of the monastery. His observations were published in an obscure Brunn journal and were overlooked for a time. His chief conclusion, stated in an elementary way, is this: If the pollen from a red flower be used to fertilize the ovules of a blue flower, and the seed thus produced be planted, one-fourth of the plants will bear red flowers; one-fourth will bear blue flowers and one-half will bear hybrid blossoms, or blossoms of mingled red and blue. Now, if the seeds of the hybrid blossoms be planted,--we might naturally expect hybrid blossoms; but here is where Mendel's law really comes in; one-fourth of the plants thus produced will bear red flowers; one-fourth blue flowers, and one-half will bear hybrid flowers. Seeds of the red and of the blue flowers produce plants bearing red and blue flowers respectively, but the hybrids tend to split up into pure bred forms.

The tendency may be expressed in a table. Let us suppose that each seed produces a plant, and that each plant bears a single flower producing four seeds. If we plant the seeds of a single hybrid flower, and continue to plant all the seeds for five generations, we shall have flowers as follows:

The hybrids split into reds and blues, so that they only double in each generation; while the reds and blues not only quadruple, but they gain from the hybrids. The hybrids are one-half of the first crop, but they are only one-thirty-second of the fifth crop, and in a few more generations they become an insignificant part of the whole. The conclusion is that pure types tend to run out hybrids; or put in another way, hybrids tend to go back--to split up into pure strains.

Another portion of Mendel's law may be illustrated without a formal statement. If we are studying a hybrid of red and blue, and red be a strong, decided characteristic while the blue is of a delicate quality, red will predominate in the hybrid and three-fourths of the flowers of the first planting will be red or dominated by red, while the more delicate blue is characteristic of one-fourth only. In such case, blue is indicative of pure blood, while we cannot tell from color alone and without planting whether a red flower be a pure red or a hybrid. In such cases, red is called a dominant quality; blue is a recessive quality.

Mendel carried on observations covering many points other than the colors of petals. He observed differences in the form of ripe seeds,--wrinkled, smooth; color of seed albumen--yellow, orange, green; color of seed coat--gray, white, brown, spotted; form of ripe pod--inflated or compressed between seeds; color of unripe pod--light green, dark green, yellow; position of flowers; length of stem--nine inches to seven feet; etc.