THE FACTORS 



CHAPTER I 

 WATER 



I. The Vegetative Organs of Terrestrial Plants. i. Genera! Considcratiotis. 

 Hygrophytes and xeropliytes. Ombrophoby and ombropliily. Physical and physiological 

 dryness. Characters of tropophytes. Climatic and edaphic xerophytes, hygrophytes, and 

 tropophytes. ii. Xerophytes. Factors reducing the absorption of water. Factors 

 favouring transpiration. Xerophilous structure. Protective means against the loss of 

 water. Correlations among xerophytes of different habitats. \\\. Hygropliyfes. Wiesner's 

 and Lotheliers researches Hygrophilous structure. Removal of superfluous water: 

 dripping points, hydathodes. iv. Tropophytes. Tropophilous structure. Leaf-fall. 

 2. Vegetative Organs of Aquatic Plants. Change in structure of submerged terres- 

 trial plants. Characteristics of true aquatic plants. 3. Water and Reproduction. 

 Hostile influence of moisture on sexual reproduction. Sexual reproduction in aquatic 

 plants. 4. Water and the Dispersal of Seeds. Adaptations of fruits and seeds for 

 dispersal by water-currents. Marine drifts. The new flora of Krakatoa. 



No factor affecting plant-life is so thoroughly clear as the influence of 

 water. From its entrance to its exit, the transpiration-current may be 

 followed, step by step ; the physiological processes of the intake, conduc- 

 tion, and exit of water have in many respects been explained ; the structure 

 of the organs concerned in these processes and in storing water have been 

 accurately investigated ; and the theory of the co-opdration of all these 

 factors is practically completed. In demonstrating, therefore, the share 

 taken by climate and soil in causing the characteristics of the vegetation of 

 any region, water claims a foremost place in our consideration. 



I. THE VEGETATIVE ORGANS OF TERRESTRIAL PLANTS. 



i. GENERAL CONSIDERATIONS. 



The absorption and emission of water by plants depends on external 

 conditions. In nature, however, these are very varied, and, in harmony 

 with the adaptability of the organisms, call forth very varied contrivances 

 Tor regulating the passage of water through a plant. The structure of 



