NUTRITION. THE MACHINERY. 33 



from the plants grown with various manures were less 

 uniform, and need not here be cited, the object being 

 merely to illustrate the large quantity of water evaporated 

 and its gradual increase with the development and growth 

 of the plant and the advance of the season. While the 

 precise effect of any particular manure in promoting either 

 absorption or transpiration is not fully known, it has been 

 shown that the alternate use of pure water and of manure 

 water has resulted in a large proportionate amount of water 

 being absorbed and transpired by the plant, and a greater 

 development of the plant than is the case where either 

 fluid is applied alone (Vesque). 



Summary. The main functions of the leaf may, there- 

 fore, be stated to be the reception and emission of gases 

 now this, now that, according as it is exposed to light or 

 darkness and the absorption and emission of watery 

 vapour. The result of all these varied processes now 

 acting together and in unison at other times in an- 

 tagonism as it were is the nutrition of the plant, the 

 building up of its structure, the formation of most of those 

 ingredients which render a plant sightly or useful. The 

 importance of these processes may be summed up in the 

 words of an eminent physiologist (Gardeners' Chronicle, 

 1881, Feb. 5, p. 169) : " All the labour of the plant by 

 which out of air, water, and a pinch of divers salts scattered 

 in the soil, it builds up leaf and stem and roots, and puts 

 together material for seed or bud or bulb, is wrought and 

 wrought only by the green cells which give greenness to 

 leaf and branch or stem. . . We may say of the plant 

 that the green cells of the green leaves are the blood there- 

 of. As the food which an animal takes remains a mere 



