THE STUDY OF NATURAL SELECTION 139 



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 pro- 

 duce 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 32 that a 

 larger proportion of doubles can be obtained from old than from re- 

 cently 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 germi- 

 nation as time goes on. 



Saunders 33 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 de- 

 creased by keeping the seeds for long periods of time, the proportion of 

 doubles increased. She also found that when, through unfavorable con- 

 ditions, 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 : 



Percentage Doubles in : 

 Variety Low Germination High Germination 



Marine blue 72.0 51.5 



Light purple 59.5 52.5 



While Miss Saunders results seem fairly conclusive the difficulties 

 of the problem are, as she points out, considerable. A careful experi- 

 mental 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. 84 



Seedling Characters and Survival. — Having shown that the meas- 

 urable 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. 85 That plants 



"See Goebel, Pringheim's Jahrb. Wiss. Bot., 17: 285, 1886, for references. 



83 E. E. Saunders, "Further Studies on the Inheritance of Doubleness and 

 Other Characters in Stocks," Appendix I., Journ. Gen., 1: 361-367, 1911. 



M Experimental work along the lines suggested by de Vries 's discussion, 

 "Species and Varieties," 2d ed., pp. 329-339, would be most important. 



M E. Baur, ' ' Untersuchungen liber die Erblichkeitsverhaltniss einer nur in 

 Bastardform lebensfahigen Sippe von Antirrhinum ma jus," Ber. Deutch. Bot. 



