VI CONTENTS. 



CONVERSATION IV. 



ON LEAVES. 



Expansion of Leaves. Sessile and Articulated. Pores, or Stomats . 

 Leaves divided into five Classes: 1. Permated ; 2. Palroated; 3. 

 Peletated; 4. Pedalated; 5. Simple Ribs. Dissected Leaves. 

 Compound Leaves. Stipula. Succulent Leaves. Seminal Leaves, 

 or Cotyledons. Prirnordal Leaves, Bracteas, or Floral Leaves. 

 Radical Leaves. Arrangement of Leaves on the Stem. Of Buds ; 

 scaly or naked ; of three descriptions of Germs ; various Modes in 

 which the leaves are folded within the Bud. Deciduous Leaves. 

 Evergreens. Fall of the Leaf. ..... 53 



CONVERSATION V. 



ON SAP. 



Sap absorbed by the Roots. Bonnet's Experiments on the Ascent of 

 Sap through the Stem. Spring Sap to Feed the Buds. Exhalation 

 by the Leaves. Quantity of Water Exhaled. Chemical Changes 

 which take place in the Leaves. Purification of the Air by Plants. 

 Sennebier's and De Saussure's Experiments. Oxygen given out, and 

 Carbon retained, by Plants. .... . -69 



CONVERSATION VI. 



ON CAMBIUM, AND THE PECULIAR JUICES OF PLANTS. 



Cambium descends through the Liber ; its descent accelerated by Agitation . 

 Mr. Knight's Experiment. Effects of Stakes and Ligatures. 

 Of the Annular Incision. Composition of Cambium. Water com- 

 bined in Plants. Internal Secretions from Cambium. Milk. Re- 

 sins. Gum. Gum Resin. Manna. Essential Oil. Fixed Oil. 

 Excretory Secretions from Cambium. Vapor of Fraxinella. 

 Odors of Plants. Bloom of Fruits. Glands of Excretory Or- 

 gans. 84 



CONVERSATION VII. 



ON THE ACTION OF LIGHT AND HEAT ON PLANTS. 



Light enables Plants to decompose Carbonic Acid ; produces their green 

 Color ; increases Absorption ; increases Evaporation. Effects of 

 Intensity of Light. Effects of Deficiency of Light. Action of 

 Heat on Plants. Effects of Deficiency of Heat. Freezing of 

 Plants. - - - - - - - 99 



