VES, 
a be a coefficient that defines the rate of development so that the 
reciprocal of « defines the longevity of the plant; 
n be a coefficient that defines the sensitiveness of the plant to tem- 
perature, so that as increases a given change in wv has a less effect 
on the rate of growth and therefore the plant can flourish in a wider 
range of temperature; therefore its geographical distribution may 
be wider, hence Coutagne calls 7 a coefficient of ubiquity ; 
c be the temperature at which the most rapid development is possi- 
ble under the most favorable conditions of growth or the temperature 
optimum; plants with a large value of ¢ must live nearer the equator 
than those having small values of c; therefore ¢ is called the index 
of tropicality. - 
According to Coutagne these quantities are bound together by the 
formula: 
This formula represents the momentary rate of development, so 
that the total duration of the growth is to be found by integrating 
this expression, which result is written as follows: 
Van Tieghem, like Coutagne and others, finds that for each special 
phase of vegetation, germination, heading, flowering, or ripening, and 
for each age of a perennial plant there exists a special relation 
between the temperature, the light, the moisture, and the chemical 
composition of the soil and water that is most favorable to growth. 
We have, therefore, to decide whether the same formula of develop- 
ment can represent the growth in each of these phases as well as 
throughout the whole career of the plant. As we have before said, the 
plant can only rearrange the inorganic products that it receives and 
develop its own structure by utilizing the molecular energy contained 
in the sunshine or some equivalent hght. Its growth does not depend 
upon any force contained within the plant nor on the temperature, as 
such, but on the quality of the radiation; therefore any formula that 
considers temperature only must be a very imperfect presentation 
of the growth, especially in those stages subsequent to the full develop- 
ment of the leaf and flower. 
Lippincott (1863, p. 506) gives a few items relative to the phenol- 
ogy of wheat in America and the origin of the varieties known as 
Lambert’s Mediterranean China (or Black Tea), Hunter’s, Fenton, 
Piper’s, which were all due to judicious selection and careful culture. 
The average wheat crop of England is stated to be 36 bushels per 
acre and that of the United States 15 or less, which large difference 
is, he thinks, the result of judicious cultivation and care in the choice 
