Page:Popular Science Monthly Volume 77.djvu/348

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By Professor E. M. EAST


THE word hybridization has been used with many meanings. The term is used here to denote the crossing of any two plants that differ from each other in a heritable character, whether they are of the same or of different species.

There is intimate connection between the rôle of hybridization and the rôle played by selection. It comes about in this way. Inherited variations are produced by nature with considerable profusion. New characters appear and old characters are lost: these form the working basis of selection. But whether they are large or small they are usually inherited completely. They are the units of heredity; or, if they are sometimes transmitted in units of lesser degree, they may be compared to chemical radicals.

The main object of hybridization then is the shuffling of these units in the first hybrid generation and their recombination in the next generation. There are, however, various phenomena attending hybridization, and I will endeavor to illustrate the following as those of most importance: (a) Recombination of characters and their fixation, (b) production of desirable combinations in the first hybrid generation and their continuation by asexual propagation, (c) production of fixed first generation hybrids, (d) production of blends.

If we begin at the real beginning in this discussion, we must say a few words concerning the actual mechanical operations of crossing. The first foundation stone to be laid is a knowledge of the flowering habits and flower structure of the plants to be used. Of course a careful examination of the flowers will show the easiest and surest method of removing the stamens of the flowers that are to be pollinated and of protecting them from foreign pollen. What is not so easily determined are the precise conditions under which the cross should be made to be successful. The proper preparation of the breeding plot even before the plants are grown is necessary. One takes it for granted that some fertilizer will be used, for the plants must be normal to seed well. The three essential elements of soil fertility are nitrogen, potassium and phosphorus, and to get the best results compounds of these elements must be present in proper proportions. First, available potash must be

  1. This paper is based on one of a series of popular lectures delivered at the Bussey Institution of Harvard University, April and May, 1910.