Page:Popular Science Monthly Volume 66.djvu/213

Rh "In some directions the strains of heredity are much more unbalanced than in others. An impulse from outside forces may bring about new combinations. This is illustrated by De Yries by a ball with many facets, which, if lightly touched, will return to its original position, if vigorously touched will turn over. Burbank once crossed a pole bean (Phaseolus vulgaris) with a lima bean (Phaseolus lunatus var. macro-carpus). There was no visible effect in the appearance of the pod or the bean, but, when planted, each bean developed a cotyledon, part of one species and part of the other. The lima bean represented the end of the cotyledon, and was united to the lower part by serrated edges; below was the smaller and striped cotyledon of the pole bean. The cotyledons finally parted at the joints between the two, the upper portion falling off, as is often the case with grafts which are uncongenial. The forms were tremendously vigorous, but all came back to the common pole or horticultural bean after the second generation, as though it were an uncongenial graft hybrid, the alien portion being finally entirely rejected. It often happens in grafting, that the branch will be united thoroughly at the point of grafting, but in great stress,. as the overbearing of fruit, the grafted portion will separate and entirely fall off."

"In one sense, hybridization is only a mode of grafting, both being a more or less permanent combination. The different results from hybridization are shown in the diagram below."

"Where the plants are very different, having a different line of descent, and consequently different structure, there will be no hybridization at all. From this we have every gradation to the point where the individuals are very closely alike, and here we have scarcely any variation at all in the progeny, a condition which favors extinction. Again, in grafting, we have every intergradation between total inability to unite and absolutely perfect blend."

"Sometimes a graft strengthens a plant by increasing the body of foliage and thus strengthening the roots. Grafting a Japanese pear on the Bartlett pear will give the latter new life through the increase in the foliage, which gives material for root action and further extension."

As illustrations of the results of crossing and hybridization, the following notes were taken on plants in Mr. Burbank's gardens:

In the beginning of his work Mr. Burbank crossed all sorts of beans and had a half acre of them. Some climbed to the height of twenty or thirty feet, producing all sorts of pods—some with pods long and slender and stems so short that the pods doubled up on the ground. These forms could have been fixed in time, though the variations were unusually persistent and very amazing in their variety and abundance.

Crossing the red and white pole bean, two or three of the beans grew large and bore striped pods, the beans themselves being jet black.