41 



in the speed with which it perfects its own growth. It seems to 

 Pauchon that we may properly interpret this phenomenon if we 

 admit that a seed transported from the north to the soutli finds itself 

 in climatic conditions more favorable to the development of the 

 embryo which it contains and of the plant which is to follow. What 

 the action of light loses in duration in proportion as we move toward 

 the equator it gains in intensity. It may be that the cause of this 

 increased activity is due to the larger size of the northern seeds or to 

 their greater richness in the essential oils. Pauchon thinks that the 

 embryo of such a seed should not be compared to a more perfect 

 machine; it is rather an identical machine, but better nourished by 

 the reserve of combustible and nutritive material in the perisperm. 

 Possibly the abundance of essential oils contained within the seed 

 contributes to furnish to the embryo in northern countries the mate- 

 rials for the oxidation that is necessary in order to maintain its tem- 

 perature during germination and to struggle against the severity of 

 the climate. 



Tisserand (1876) has shown that the rye cultivated in northern 

 Norway has not the same chemical composition as that of France and 

 Algeria, and that in general, as we go northward, or as we rise above 

 the level of the sea, or as the temperature lowers without diminishing 

 the quantity of light, we see the starch in the grain increase relatively 

 to the nitrogenous components. Wheat grown at Lynden ( North Cape) 

 has a smaller proportion of gluten than the wheat of France, and the 

 latter less than the wheat of Africa. On the other hand, barley 

 raised at Alten, on being sown at Vincennes on the 7th of April by 

 Tisserand, was ripe on the 18th of June, or thirty-seven days in 

 advance of French barley, so that in order to mature it required a 

 sum total of heat far less than the French barley. The reverse is 

 true when southern grains are carried north and sown in colder 

 climates. Therefore, as Marie-Davy has remarked, plants become 

 acclimated more or less rapidly according to their own nature and 

 the extent of the climatic variations that are imposed upon them; the 

 climate produces in them a functional change which corresponds to 

 an organic change the nature of which often escapes our observation. 

 It is therefore not necessary that each phase of vegetation should 

 corresj3ond to a constant sum of heat in very different climates. 

 That which it is important for us to know is what are the limits 

 between which this sum total can vary, for the same s})ecies of i)lant 

 under different climates. 



The general fact that the quantity of nitrogen contained in the 

 seeds increases as we approach the warmer climates leads to the 

 hypothesis that the formation of albuminous reserves within the seed 

 takes place in proportion to the temperature, and that the formation 

 of starch and other reserves takes i^lace in proportion to the duration 



