CHAPTER II 



ASSIMILATION AND TRANSPIRATION 



§ I. Significance of Assimilation and Transpiration. § 2. The Leaf. 

 § 3. Relation of the Stomata to Gaseous Exchange. § 4. Distri- 

 bution and Dimensions of Stomata. § 5. Diffusion through the 

 Stomata. § 6. Stomatal Movements and their Mechanism. § 7. 

 Gaseous Exchange of Aquatics. § 8. Gaseous Exchange of Succu- 

 lents. § 9, Energy Relations of Assimilation. § 10. Orientation 

 of the Leaf and Illumination. § 11. Mechanism of Leaf Adjust- 

 ment. § 12. Orientation of Strongly Insolated Leaves. § 13. Leaf 

 Structure and Assimilation. § 14. Chlorophyll and Absorption of 

 Light. § 15. Chlorophyll in its Relation to Assimilation. § 16. 

 E.xternal Conditions and Assimilation. § 17. Assimilation in Natural 

 Environment. § 18. Extent of Transpiration. § 19. Water Balance, 

 Wilting, and Water Storage. § 20. Atmospheric Conditions and 

 Transpiration. § 21. Stomatal Regulation. § 22. Regulation by 

 Internal Leaf Changes. § 23. Limitation of Transpiration by Form 

 and Position of Stomata and by Cuticle. § 24. Hairiness and Tran- 

 spiration. § 25. Effect of Ethereal Oils. § 26. Number of Stomata. 

 § 27. Reduction of Leaf Surface and Tianspiration. § 28. Moor- 

 land Xerophytes. § 29. Leaf Reduction : Transference of Assimi- 

 lating Function. § 30. Transpiration of Succulents. § 31. Assimi- 

 lating Roots. § 32. The Significance of Xerophytism. § 33. 

 Promotion of Transpiration. § 34. Functions of Transpiration. 

 § 35. Inter-relation of Transpiration and Assimilation. 



§ I. Significance of Assimilation and Transpiration 



Assimilation. — The possession of that complex of four 

 pigments which we call chlorophyll is the fundamental 

 attribute of the plant kingdom. From the unicellular alga 

 to the flowering plant chlorophyll is found without essential 

 change. Such exceptions as the copper beech are apparent 

 only, the green pigment being present, though masked by 

 red sap anthocyans. In the two great groups of red and 

 brown algae, chlorophyll is associated in the chloroplasts 

 (special organs of the protoplasm) with other pigments 

 which modify the colour. In all the flowering plants so far 



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