Page:Popular Science Monthly Volume 84.djvu/143

Rh most important case is undoubtedly that of single and double stocks. Double stocks are completely sterile, forming neither ovules nor pollen. They must, therefore, be propagated exclusively by seeds from singles. In the effort to place on the market seed which will produce the highest possible proportion of doubles, the closest attention has been given to all factors—shape and color of seed, position of the seed in the pod, position of the pod on the plant, etc.

At the beginning of the last century, the belief was current that a larger proportion of doubles can be obtained from old than from recently harvested seed. Apparently, the original idea was that the transformation took place in the harvested seed, but Goebel suggested that its foundation may lie in a differential viability, the seeds which would have produced singles losing more and more their power of germination as time goes on.

Saunders seems to have put the empirical conclusion and Goebel's interpretation on a scientific basis. In actual experiments which need not be detailed, she found that as the percentage of germination decreased by keeping the seeds for long periods of time, the proportion of doubles increased. She also found that when, through unfavorable conditions, the seeds were of a poor quality and a high percentage failed to germinate, the proportion of doubles was greater. Thus if the pods of 1909 be classified in two groups according to whether they produced less than fifty per cent, or fifty per cent, or more seedlings, we find for two strains:

While Miss Saunders results seem fairly conclusive the difficulties of the problem are, as she points out, considerable. A careful experimental investigation on a large scale of the viability of the seed in double stocks and in other ever-sporting varieties would be of the greatest interest.

Seedling Characters and Survival.—Having shown that the measurable characteristics of the apparently normal seed, or the invisible potentialities of its embryo, may be of importance in determining its viability, i. e., that they may be of "selective value," one next inquires whether in the young plantlet some variations tend to be weeded out.

We are indebted to Baur for a neat demonstration. That plants