PLANT NUTRITION. 37 



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 

 vapor. The result of all these varied processes now act- 

 ing together and in unison at other times in antagonism 

 as it were is the nutrition of the plant, the building up 

 of its structure, the formation of most of those ingre- 

 dients which render a plant sightly or useful. The im- 

 portance of these processes may be summed up in the 

 words of an eminent physiologist (" Gardeners' Chroni- 

 cle," 1881, Feb. 5, p. 169) : " All the labor 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 thereof. As the food which an 

 animal takes remains a mere burden until it is transmut- 

 ed into blood, so the material which the roots bring to 

 the plant is mere dead food until the cunning toil of a 

 chlorophyll-holding cell has passed into it the quickening 

 sunbeam. Take away from a plant even so much as a 

 single green leaf, and you rob it of so much of its very 

 life blood." A warning this against the premature re- 

 moval of leaves, as when leaves are taken from the bulbs 

 of our mangels before they have completed their work of 

 formation and accumulation. 



In this, and other matters, however, the cultivator 

 often has to make a compromise, and act as is best for 

 himself under the particular circumstances of the time. 

 It is not the good of the plant that he seeks in the first 

 instance, but only in so far as it contributes to his own 

 profit ; and although in principle every injury needlessly 

 inflicted on a plant must in the long run be injurious, it 



