Page:Popular Science Monthly Volume 66.djvu/207

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203
SOME EXPERIMENTS OF LUTHER BURBANK.

Not many of Mr. Burbank's results are due to unassisted selection, as the processes of crossing and hybridization save time by the increase of the rate or degree of variation. There is, however, no evident limit to the results to be obtained by simple selection. New and permanent species of wheat have, without a shadow of doubt, been produced by selection alone.

In the California poppy (Eschscholtzia californica), stripes of crimson are never seen on the inside. Mr. Burbank once found a seedling in which the outside crimson had struck through like a crimson thread which had been misplaced. In other generations, by selection, this red was more and more increased, until finally out of it is developed a crimson poppy, of which Mr. Burbank has now many specimens, seeding more or less true to the type. The 'Shirley' poppy (Papaver rhæas) is well on the way to blue by selection.

It is questioned whether competition in minor details, or 'intraspecific selection' can form species permanent as wild species are. As to this, Mr. Burbank notes that the cultivated species produced after the fashion of his crimson eschscholtzia 'have a very brief history compared with the wild species, and, moreover, they are constantly being placed in a new environment by man, being influenced by new soils, new climates, new fertilizers and the like. "Breeding to a fixed line will bring fixed results. Man's desultory breeding is brief, the struggle for existence is mostly absent, and new ideals and new uses are required instead of ability to endure under natural conditions. Man's efforts at selective breeding are fluctuating, with frequent saltations."

Dr. De Vries notes that in the common sugar beet, which is a biennial species, there are from one to ten per cent, of plants which bear seed the first year. None of these is ever chosen for seed, and yet the long-continued process of natural selection has never succeeded in rooting them out. As to this Mr. Burbank observes: "This long-fixed tendency to insure continued existence in the past is not yet bred out. Analogous to this is the tendency in flocks to produce black sheep, and the appearance of zebra stripes on horses—ancestral traits not yet bred out."

From the pale yellow Iceland poppy (Papaver nudicaule) are developed white, yellow and orange forms, and some with striped petals and a strong tendency to become double. Selecting the Iceland poppy for size alone, flowers three and one-half inches across have been developed. A large scarlet poppy, Papaver glaucum, closes its two inner petals when a bee or two have entered, shutting in the bees, which buzz angrily and cover themselves with pollen until they are set free. If not visited by bees, the flowers do not close.

A wild form of one of the Liliacæ, Brodiæa terrestris, was made white by selection of the palest among the pale wild ones. Brodiæa