80 PLANT LIFE ON THE FARM. 
of their contents, which are thus forced upwards towards 
the upper part of the stem. Ina very dry, hot season, 
when the light is intense, evaporation and life-action 
generally go on too rapidly, and the harvest is deficient ; 
on the other hand, if the summer is wet and the light 
deficient, maturation is imperfect, the transport of nu- 
tritive matters from leaves upwards to the fruit and 
seeds is checked, the younger leaves do not draw upon 
the lower ones, and the season, though favorable to for- 
age crops, is not so propitious to grain crops, to fruit 
ripening, or to timber in which a deposit of woody 
material in the cells is essential. 
Ripening of Fruits.—The ripening of fruits, such as 
those of the apple and pear is attended with a series of 
chemical changes which can here only be cursorily allud- 
ed to. While the fruit remains green, it acts precisely 
as a leaf does. As it ripens its color changes ; it no lon- 
ger decomposes carbonic acid and gives off oxygen in the 
daylight, but it utilizes the oxygen of the carbonic acid 
to oxidize and burn up the vegetable acid and the sugar 
which the fruit contains. Subsequently the sugar under- 
goes a species of alcoholic fermentation, characterized by 
the emission of carbonic acid gas and by the formation 
of alcohol, which latter, uniting with the acid of the 
fruit, produces ethers of various kinds, to which the 
peculiar odor and flavor of the fruit are due. 
The processes of maturation and fruiting therefore are 
not dependent upon the mere accumulation of. food ; 
otherwise by increasing the quantity of manure and ap- 
plying it continuously we should increase the crop. As 
a matter of fact we know we should not do so, and that 
the effect of over-feeding under such circumstances would 
be to render the plant unhealthy by preventing it from 
assimilating and maturing. Similarly we know from ex- 
perience that heat alone is not sufficient to induce 
