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 south 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 
correspond 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 species of plant 
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 place in proportion to the duration 
