CONTENTS. 



IX 



Conditions of growth. 



I. Proper medium and space for growth . . . . .61 

 Uses of the soil — 1. Support 61 



2. Repository of food. 3. Chemical changes, medium of . 61 



4. Medium for air, water and heat . . . . .62 



5. Absorption of gases ........ 62 



II. Food. Supply of food. 



1. Constancy of supply 63 



2. Proper regulation ........ 63 



Practical inferences 64 



3. Kind of food — nature of 65 



III. Tillage — Conditions of 66 



1. Thorough ploughing ........ 66 



2. Deep ploughing, importance of . . . . . .67 



3. Pulverizing the soil 68 



4. Covering the seed ........ 68 



.5. Extermination of weeds ....... 69 



Importance of the above conditions illustrated . . . .70 



CHAPTER II. 



INFLUENCE OF THE ATMOSPHEKE, WATER AND OTHER AGENTS, UPON 

 THE VITAL PRINCIPLE, AS CONNECTED WITH THE PHENOMENA OF 

 VEGETATION. 



Sect. 1. JJgejicy of the atmosphere. 

 Composition of the atmosphere .... 

 I. Influence of the oxygen of the air upon the roots 



Theories 



Influence of oxygen upon the leaves of plants . 



Theories 



Quantity of oxygen absorbed by plants, dependent, 



1. Upon their vigor 



2. Upon temperature 



3. Upon the season of the year 

 Quantity absorbed by the fleshy-leaved plants 



" " evergreens 



" " herbaceous plants 



" " trees naked during the winter 



Action of oxygen upon fruit .... 



Summary of the agency of oxygen 

 II. Influence of the nitrogen of the air 



72 



73 

 73 



75 

 76 



76 

 76 

 76 

 76 



77 

 77 

 77 

 78 

 79 

 80 



