80 PLANT LIFE ON THE FARM. 



of their contents, which are thus forced upwards towards 

 the upper part of the stem. In a yery 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 



