THE CABBAGE THAT WED A RADISH

Mate a donkey and a horse, and you get nothing but mules. Mate a carrot and a beet, and you get—nothing at all. The relationship is too remote. For the breeder, the rule is always make sure your matings are relatively close; the more distant the cousinship, the less chance you have of obtaining offspring, and the less chance the offspring you do get have of amounting to anything. There are a few good hybrids that have become standardized—the mule for example—but for every success resulting from these out-of-the-family matings, there are thousands of failures. The great majority of hybrids are worthless.

It was so with the radish-cabbage wedding that took place under Dr. Karpechenko's hand in the garden of the Institute of Applied Botany at Detskoe Selo, near Leningrad. The offspring were neither cabbages nor radishes, but merely queer rosettes of leaves. They did not make cabbage heads above the ground nor radish roots beneath. In fact, they resembled, outwardly at least, the tufty little ancestral cabbage plants that still grow wild on the cliffs along the North Sea shores. That is the fate of many hybrid crosses; they produce what look like "throwbacks."

Yet in spite of the unpromising looks of the radish-cabbage children, Dr. Karpechenko cultivated them carefully, saved such seed as they formed, and took tender care of the grandchildren plants also, though they turned out no better than their parents.

EINSTEIN UNITES GRAVITY AND ELECTRICITY

Since the days of Maxwell, over 50 years ago, we have had a mathematical theory of electricity and magnetism due to Maxwell which gives a fairly satisfactory account of the principal electrical and magnetic phenomena. And since Einstein published his general theory of gravitation, now some 12 years ago, we have had a similar mathematical theory for gravitational phenomena. These two theories bear no apparent resemblance to each other.

It is a physical fact that gravitation bears a close resemblance to electric and magnetic attraction in that all these forces act according to the inverse square of the distance, and there has been for many years a branch of mathematical physics (Theory of Potential) which handles the elementary phenomena of gravitation, electricity, and magnetism by the same identical mathematical treatment. This theory, however, cannot go far, as there is one important feature in which gravitation differs from electricity and magnetism. There is no screen or insulator for gravitation.

Einstein seems to have developed a general mathematical theory for all three of these physical manifestations, which includes as special cases Maxwell equations and his own gravitational theory and automatically provides for the important difference above mentioned—the absence of a screen for gravitation.

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