|;-|() Gates, Tetraploid Mutants and Chromosome Mechanisms. 



yiyas Sweden the mature capsules are very long and contain many 

 more seeds than in gigas Italy. But in this case the ovaries ready 

 for fertilization are extremely long and probably contain more 

 ovules, so that the percentage of sterility may be no less than in 

 gif/as Italy. De Vries cites (4) the outgrowth of the axillary buds 

 on the stem to form branches, as another difference. But this is 

 an extremely variable character both in gigas, Lamarckiana and 

 the other forms, depending no doubt upon local environmental condi- 

 tions at the time when these various buds reach a certain stage 

 of development. It can therefore scarcely be considered a constant 

 differentiating mark from Lamarckiana. 



Another interesting physiological difference noted in the gigas 

 races during the past season was their greater susceptibility to 

 frost. On the morning (Oct. 5) after a rather heavy frost, the flowers 

 and unopened buds of the gigas races were bitten and drooped 

 over, while all the diploid races in the garden escaped. The only 

 exception was the small-flowered plant of gigas Italy (227. I. 4), 

 which was unaffected. This difference again is no doubt a result 

 of the larger size of the cells in gigas. 



Since it is possible to explain easily so many apparently diverse 

 morphological and physiological characters in gigas as the result of 

 a single initial change in nuclear structure and consequently in 

 cell size, one must hesitate before affirming that any character of 

 gigas is necessarily the result of another (additional) change. Our 

 knowledge, or rather our ignorance, of morphogenesis is at least 

 as profound as that of the physicist who cannot explain why a 

 certain rate of ether vibration gives the sensation of red and 

 another the sensation of blue; or as that of the chemist, who cannot 

 correlate the properties, such as color and crystalline shape, of his 

 compounds, with their chemical composition except in a very limited 

 way. It is evident that many secondary changes in O. giyas, such 

 as the larger seeds and shorter capsules ; and physiological changes 

 such as the stronger biennial habit and greater susceptibility to 

 frost, follow as a result of an initial quantitative change in nuclear 

 and cell structure. According to the logical "law of parsimony" 

 one cannot introduce an additional cause to explain these changes 

 unless they can not be explained without its help, but I have 

 shown that the characters cited can be so explained. Regarding 

 the few characters of gigus, such as leaf-shape, which remain to be 

 explained, one can only say that in our present ignorance of 

 morphogenesis of the relation between organic cell structure 

 and external form - - we cannot really distinguish between quantita- 

 tive and qualitative characters, except that we do know that in 

 many cases specific differences which appear to be qualitative are 

 found when analyzed to rest upon ultimate quantitative differences. 



