CHAPTER II 
PLANT FOOD AND SOIL PROBLEMS 
By W. B. BOTTOMLEY, M.A., Ph.D. 
Professor of Botany in King’s College, London 
THE importance of a knowledge of the conditions and 
factors influencing plant growth is evident when one 
considers the intimate connection between the profitable 
exploitation of-plants and maximum crop production; 
The living plant is a synthetic machine absorbing as 
raw materials such substances as water, carbon dioxide, 
nitrates, phosphates, etc., and manufacturing them into 
‘various commercial products—foods (sugars, starches, 
proteins), timber, fibres (cotton, linen), colouring matters 
(dyes) and alkaloids (drugs)—and the value of any know- 
ledge which enables the owner to run the machine 
more economically or to increase its output cannot 
be denied. 
The soil is the source of all the raw materials, except- 
ing carbon, and at first sight the problem of maintaining 
or increasing the crop-producing power of any soil would 
appear to be a simple one. Analyses of the ashes of 
plants have shown that a certain few mineral substances 
are always present in plants, and are essential to them as 
nutrients. The importance of these has been amply 
confirmed by water and sand cultures. Obviously these 
It 
