No. 632] SHORTER ARTICLES AND DISCUSSION 



263 



recombine in the Mendelian sense, quite as do the factors con- 

 trolling the form of leaf and flower. The result is that after a 

 few generations of selection one may obtain a variety of strains, 

 uniform within each line, so fertile as to yield capsules with over 

 ninety per cent, of the normal quota of seed, and so different 

 from one another that the extreme types are more unlike than 

 the two original species used in the cross-. 



After three years of selection (F 5 ), eight such strains re- 

 mained out of a large series of selections studied earlier. It 

 seems hardly necessary to describe the differences they exhibited. 

 Suffice it to say that the smallest type was about 20 cm. in height 

 with small smooth oval leaves, and the largest was nearly 200 

 cm. in height with wrinkled cordate leaves some of which were 

 50 cm. in length. 



These eight strains were cross* d in all possible combinations, 

 and every F, (jot, rut inn (.rhihiteil as high a degree of fertilitg a* 

 that shown by the parents. 



To the writer it seems possible that these results have a bear- 

 ing on certain theoretical problems which may not be clear at 

 first sight. 



A few years ago Lotsyf published an extended paper based on 

 a very limited number of crosses in the genera Nicotkna. Pisum. 

 Petunia and Antirrhinum, where partially sterile F, plants pro- 

 duced exceedingly variable progeny,— results wholly comparable 

 with our own. From these observations, neglecting all evidence 

 of the appearance of mutations in controlled pure lines, Lotsy 

 founded a theory of evolution. His arguments were based upon 

 five assumptions: (1) that all characters obey the Mendelian law 

 of heredity, (2) that acquired characters are never transmitted, 

 (3) that homozygotes are absolutely constant in succeeding gen- 

 erations, (4) that there has been no proof of variation inde- 

 pendent of crossing, and (5) that the variations observed after 

 crossing are sufficient to account for evolution. 



Naturally numerous criticisms can be made against this ex- 

 treme interpretation. One need only inquire as to the source of 

 the original variations which are to form the basis of all Men- 

 delian recombinations, to show the untenability of the position. 

 On the other hand, it will be admitted by all that hybridization 

 has played some part in evolution, and it is of some importance 

 to endeavor to determine the limits of its role. 



2 Lotsy, J. P., "La th^orie du oroisement, " Arch. Xeerland. Sci. Exact, 

 et Nat., Ill, B, 2: 1-61, 1914. 



