CONTENTS. 



Sect. 3. Influence of the imponderable agents upon the vital func- 

 tions of plants. 



I. Gravity. Experiments of Mr. Knight 98 



II. Cohesion 99 



III. Chemical affinity 100 



IV'. Caloric. — Properties necessary to be studied • . 101 



1. Its influence on affinity 102 



2. Effect of heat in the spring — of too great heat . . 102 



3. Tendency of heat to pass into an insensible state . .102 



4. Effect of heat during the winter 103 



Distribution of plants dependent upon temperature . . 104 



V. Light. Calorific. Colorific and chemical rays . . 105 



1. Stimulating properties of light 105 



2. Its power in the decomposition of carbonic acid by the leaves 106 



3. Different colors. Experiments of Mr. Hunt . . . 106 



VI. Electricity. Modes of exciting it. Theory . . . 107 



Endosmometer, description of 108 



Cause of the ascension of the sap ...... 109 



Sect. 4. Agency of man. 

 Methods by which men may control the imponderable agents 111 



CHAPTER 111. 



PRODUCTIONS OF THE VITAL PRINCIPLE — THEIR CHARACTER, COMPO- 

 SITION, SOURCES AND ASSIMILATION, 



Sect. 1. Character and comjiosition of the vegetable productions. 



I. Acids 117 



II. Alkalies . . . 119 



III. Intermediate bodies . . 120 



IV. Neutral substances 123 



1. Sugars. 2. Amylaceous substances .... 124 



3. Gums 125 



4. Glutinous substances 126 



Sources of many articles of food and medicine .... 126 



I. Roots 128 



II. JBulbs 129 



III. Woods 130 



IV. Leaves 130 



V. Seeds and fruits 131 



