22 



GENETICS IN RELATION TO AGRICULTURE 



TABLE I. CHEMICAL COMPOSITION OF THREE 



PLANTS OP Sedum Speclabtie GROWN IN 



WHITE, RED AND BLUE LIGHT. 



and six distinct types were found, according to the variation in number 

 of stamens. These had the following average numbers of stamens: (1) 

 9.68, (2) 8.45, (3) 6.54, (4) 5.05, (5) 9.47, (6) 7.33. Finally, Klebs 

 subjected similar plants from white, red and blue light to chemical 

 analysis in order to secure further evidence of the physiological effects 

 of light of different wave lengths. Table I shows the composition 

 of the leaves in three plants like those shown in Fig. 4. They were in 

 their respective greenhouses from June 6 to September 7. The percent- 

 ages shown are per 100 g. of 

 dry substance. In compar- 

 ing these percentages it 

 should be remembered that 

 the plant in white light pro- 

 duced 1324 flower buds and 

 the plant in red light 405, 

 while the plant in blue light 

 produced none. This ex- 

 plains the higher percentage 

 of ash, nitrogen and protein 

 in the last. On the other 

 hand, the amounts of starch and sugar found in the plant from 

 white light are decidedly larger than the one from blue light. In 

 short, according to Klebs, in comparison with normal white light, 

 the production of organic substances, such as starch and sugar, 

 is diminished under the influence of blue light as microchemical 

 and macrochemical tests distinctly show. In consequence of this di- 

 minished assimilation of carbon dioxide the rosettes become purely 

 vegetative. In red light the carbon assimilation is greater than in blue 

 light but less than in white. These experiments prove that the transfor- 

 mation of a plant "ripe to flower" into a vegetative one is possible on 

 the one hand by an increase of temperature and of inorganic salts and 

 on the other hand by a decrease of carbon assimilation. 



(6) Temperature and Pigmentation. Many experiments in the rearing 

 of moths and butterflies under controlled temperatures prove that degree 

 of pigmentation is profoundly influenced by the temperature at which 

 the pupae are kept. Some species exhibit seasonal dimorphism in the 

 wild state. By taking pupae of the common European form of the 

 swallowtail butterfly, Papilio machaon, and subjecting them to a tempera- 

 ture of 37 to 38C., Standfuss obtained the characteristic summer form 

 which occurs in Palestine. Again it has been shown by temperature 

 experiments that many variations found among insects in nature are 

 merely aberrations due to temperature effects. Goldschmidt by arti- 

 ficially controlled temperatures has produced a series of forms of the 



