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THE POPULAR SCIENCE MONTHLY 



Fig. 6. 



tropism." This, however, does not give a mechanical reason for it; 

 not more so than for the left-handed spirals of snail-shells. In the 

 Rocky Mountains I have often noticed this peculiar tendency in the 

 uniform twisting of the fibers of the Lodge Pole pine. 



The plain appearance of geometric configurations and relations is, 

 of course, not limited to plant life alone; mineralogy, zoology and 

 geology also offer many examples of this kind. 



The forms of crystals, for instance, may be derived abstractly from 

 certain considerations in the theory of groups. 



Mendel's law of heredity has in recent years become of extreme im- 

 portance as a powerful means of research. 7 The abstract form of this 

 law is derived from combinatory analysis, as will appear from the 

 following experiment of L. Cuenot. 8 All individuals of the offspring 

 resulting from the crossing of the ordinary gray mouse with the albino 

 mouse are gray ; the gray element G dominates, while the white element 

 W is hidden by the gray. Crossing individuals of the offspring, among 

 the new offspring there will be gray and white specimens, and the ratio 



7 Lang, ' ' Uber die Mendelschen Gesetze, etc., ' ' Schweiz. Naturf. Gesellsch., 

 Luzern, 1905. 



8 Eevue Scientifique, Paris, 1906. 



