CONTENTS. 19 



CHAPTER Y. 



PULVERIZATION. 



A crumbling consistency of soils necessary — The importance of pul- 

 verization — Stiffness of clays — The non-retention of sandy soils — 

 Coldness of heavy earths — Summers — Injurious effects of drought 



— Example of proper valuation of arable soil — Theory of Jethro 

 Tull — Effect of insects upon pulverization — Depth — Digging 

 circles around trees deprecated — Power of extension by roots — 

 Deep cultivation affords fresh earth — Manner of operation — The 

 season — Kesults of it : rapid absorption of moisture — Free admis- 

 sion of the air — The mixture of earths — The destruction of insects 



— The increase of heat 126 



CHAPTER VI. 



FERTILIZATION. 



Selective power of plants — Form in which food is taken up — Ex- 

 cretion — Circulation of the sap — Organic substances : Oxygen, hy- 

 drogen, carbon, nitrogen — Inorganic substances — Manures adapted 

 to different soils : to clays, to peaty soils, to sandy lands — Plants to 

 be used in green-manuring — Application of manures . . 164 



