PLANT NUTRITION. 34 
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 ont 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 asa 
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 
