82 PLANT LIFE ON THE FARM. 



upper part of the stem. In a 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 nutritive 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 favourable to forage 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 alluded 

 to. While the fruit remains green, it acts precisely as a 

 leaf does. As it ripens its colour changes ; it no longer 

 decomposes carbonic acid and gives off oxygen in the day- 

 light, but it utilises 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, characterised 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 

 odour and flavour 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 applying it con- 

 tinuously 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 



