Xll CONTENTS. 



Sir J. B. Lawes and Sir J. H. Gilbert, the nature and value of 

 their experiments 33 



Review of the present state of our knowledge of plant-growth 36 

 Proximate composition of the plant . . . . .36 



Fixation of carbon by plants . . . . . .37 



Action of light on plant-growth, Dr Siemens' experiments 38 

 Source of oxygen and hydrogen in the plant . . 39-40 



Source of nitrogen in the plant . . . . .40 



Relation of the free nitrogen to leguminous plants . 42-44 



Relation of nitrogen in organic forms, as ammonia salts, 

 and nitrates to the plant ..... 46-50 



Nitrification and its conditions ...... 51 



Ash constituents of the plant ...... 53 



Methods of research for ascertaining essentialness of ash 



constituents of plants 53 



(a) Artificial soils, (6) water-culture .... 53-55 



Method in which plants absorb their food-constituents . 55 

 Endosmosis . . . . . . . . .55 



Retention by soils of plant-food ..... 57 



Causes of retention by soils of plant-food .... 59 



Manuring ......... 60 



" Field " and " pot " experimentation .... 60 



PART II. PRINCIPLES OF MANURING. 



CHAPTER I. FERTILITY OF THE SOIL. 



What constitutes fertility in a soil ...... 65 



I. Physical properties of a soil . . . . . .66 



Kinds of soils ......... 67 



Absorptive power for water of soils ..... 67 



Absorptive power for water of sand, clay, and humus . 68 

 Fineness of particles of a soil . . . . . .69 



Limit of fineness of soil-particles . . . . .69 



Importance of retentive power . . . . . .70 



Power of plants for absorbing water from a soil, experi- 

 ments by Sachs ........ 73 



How to increase absorptive power of soils . . . .74 



Amount of water in a soil most favourable for plant growth 75 

 ' Hygroscopic power of soils . . . . . .75 



Capacity of soils for absorbing and retaining heat . . 76 



