40 
These remarks of De Candolle with reference to germination are 
equally applicable to the whole period of growth of the pant. 
As to the method of calculating the sum total of temperatures 
De Candolle found that it may be conducted in two ways, either by 
adding together all the mean daily temperatures above 0° C. or by 
omitting the useless degrees and adding all the others. This last 
method would seem to be the most logical, but can rarely be 
employed, owing to our ignorance of that minimum temperature 
below which all must be omitted. On the other hand, if we consider 
that a plant which vegetates between 10° C. and 30° C. has a maxi- 
mum at 20° C., and if we seek the coefficients of growth correspond- 
ing to each successive degree of temperature, we find, as Boussingault 
has shown, that these coefficients vary for each degree as we depart 
above or below the temperature most favorable to vegetation. 
Similarly De Candolle (1865) has shown that near the minimum 
and near the maximum temperatures the rate of germination is more 
difficult, and therefore slower, than at the intermediate or best tem- 
peratures; consequently, both in germination and in subsequent veg- 
etation, it is necessary to recognize the fact that calculations of the 
sums of heat in connection with the study of the geographical distri- 
bution of plants are comphcated with hypotheses and many sources 
of error. 
Schuebeler (1862) shows that cultivated plants in northern coun- 
tries have more highly colored flowers, larger and greener leaves, and 
larger seeds, which are more highly colored and richer in essential 
oils, than those of southern regions. Bonnier and Flahault (1878) 
have shown the same facts for uncultivated plants. Both these 
authors attribute this result to the prolonged action of sunhght, 
and the latter shows that the variations are exactly proportional to 
the duration of sunlight. In Flahault’s more recent observations he 
shows that there must necessarily exist a relation between the quan- 
tity of carbonic acid decomposed and the quantity of carbonaceous 
matters formed by the plant, and that in general the sunlight has a 
very remarkable influence on vegetation since it compensates in a 
large measure for the deficiency of temperature. 
Tt is, furthermore, to this influence of ight that Pauchon attributes 
the singular fact that plants cultivated in high latitudes are endowed 
with a vegetating power greater than that of southern countries, so 
that when transported to the south their seeds ripen sooner than those 
of the southern plants. This subject has been especially studied by 
Tisserand in his memoir on vegetation in high latitudes, as cited by 
Grandeau in his work on nutrition of plants. According to Tis- 
serand a plant behaves in northern latitudes as a more highly per- 
fected machine and one that performs better than southern plants. 
In regions where it has neither time nor heat it gains in activity and 
