202 USE OF LEAVES. [BOOK 11. 



CHAPTER VII. 



OF THE LEAVES. 



LEAVES are at once organs of respiration, digestion, and 

 nutrition. They elaborate the crude sap impelled into them 

 from the stem, decomposing its water, adding to it carbon, 

 and exposing the whole to the action of air ; and while they 

 supply the necessary food to the young tissue that passes 

 downwards from them and from the buds, in the form of 

 alburnum and liber, they also furnish nutriment to all the 

 parts immediately above and beneath them. 



There are many experiments to show that such is the 

 purpose of the leaves. If a number of rings of bark are 

 separated by spaces without bark, those which have leaves 

 upon them will live much longer than those which are 

 destitute of leaves. If leaves are stripped from a plant before 

 the fruit has commenced ripening, the fruit will fall off and 

 not ripen. If a branch is deprived of leaves for a whole 

 summer, it will either die or not increase in size perceptibly. 

 The presence of cotyledons, or seminal leaves ; at a time when 

 no other leaves have been formed for nourishing the young 

 plant, is considered a further proof of the nutritive purposes 

 of leaves : if the cotyledons are cut off, the seed will either 

 not vegetate at all, or slowly and with great difficulty; and 

 if they are injured by old age, or any other circumstance, 

 this produces a languor of habit which only ceases with the 

 life of the plant, if it be an annual. This is the reason why 

 gardeners prefer old melon and cucumber seeds to new ones : 

 in the former the nutritive power of the seed-leaves is impaired, 

 the young plant grows slowly, a languid circulation is induced 

 from the beginning ; by which excessive luxuriance is 

 checked, and fruit formed rather than leaves or branches. 



Nothing can be more admirable than the adaptation of 



