5 8 PROBLEMS OF GENETICS 



on the same stem, they come off alternately. But if, as in the 

 seedlings of Barley the twist of the first leaf be examined, it 

 will be seen to be either a right- or left-handed screw. An 

 ear of barley, say a two-row barley, is a definitely symmetrical 

 structure. The seeds stand in their envelopes back to back in 

 definite positions. Each has its organs placed in perfectly 

 definite places. If these seeds were buds their differentiations 

 would be grouped into a common plan. One might expect that 

 the differentiations of these embryos would still fall into the 

 pattern; but they do not, and so far as I have tested them, any 

 one may be a right or a left, just as each may carry any of the 

 Mendelian allelomorphs possessed by the parent plant, without 

 reference to the differentiation of any other seed. The fertil- 

 isation may be responsible, but our experience of the allelo- 

 morphic characters suggest that the irregularity is in the egg- 

 cells themselves. 19 



Germ cells thus differ from somatic cells in the fact that their 

 differentiations are outside the geometrical order which governs 

 the differentiation of the somatic cells. I can think of possible 

 exceptions, but I have confidence that the rule is true and I 

 regard it as of great significance. 



The old riddle, what is an individual, finds at least a partial 

 ,-solution in the reply that an individual is a group of parts dif- 

 ferentiated in a geometrically interdependent order. With the 

 germ-cell a new geometrical order, with independent polarity is 

 almost if not quite always, begun, and with this geometrical inde- 

 pendence the power of rejuvenescence may possibly be associated. 



The problems thus raised are unsolved, but they do not look 

 insoluble. The solution may be nearer than we have thought. 

 In a study of the geometry of differentiation, germinal and 

 somatic, there is a way of watching and perhaps analyzing what 

 may be distinguished as the mechanical phenomena of heredity. 

 If any one could in the cases of the Picotee and the Bizarre Carna- 

 tion, respectively, detect the real distinction between the two 



19 Remarkable experiments on this question have lately been carried out by 

 R. H. Compton (Camb. Phil. Soc, XV, 19 10, p. 495). showing that in a certain 

 Barley, "Plumage Corn," the average ratio of left to right is about 1.5. A fuller 

 paper has since been published by Compton, Jour. Genetics, 191 2, II, 1, p. 53* 

 Compare also the case of Arum spathes examined by Christy, Jour. Bot., 191 4« 

 jiii, p. 258. 



