SECTION III 



ADAPTATIONS OF AQUATIC AND TERRESTRIAL 

 PLANTS. OECOLOGICAL CLASSIFICATION 



CHAPTER XXVII. AQUATIC AND TERRESTRIAL PLANTS 



In the Introduction ^ brief mention was made of the fact that there 

 are plant-communities which are characterized by a definite physiognomy, 

 definite constituent growth-forms, and a definite economy : this is a 

 consequence of the circumstance that those species which make approxi- 

 mately the same demands in regard to the nature of the environment, 

 or which are associated for other reasons, congregate naturally to consti- 

 tute a kind of single entity. 



It will now be our task to inquire as to what communities there are, 

 and on what principles they are to be most naturally defined and ranged 

 into some sort of system, or, in other words, which of the factors men- 

 tioned in Section II are of the greatest significance in this matter, and 

 which of them play only a subordinate role, also what part in the estab- 

 lishment of this classification is taken by the growth-forms already dis- 

 cussed in Section I. Before we can deal with the individual communities 

 we must consider oecological classification as a whole. 



The grouping of the classes of communities here adopted is based 

 in the first place upon the -plants dependence upon and relation to 

 water?' Pindar's aphorism, apirrrov ixev vboip, is wholly true of plant- 

 life ; water is the condition of life that exercises the greatest influence 

 in bringing into being external and internal differences among plants ; 

 it is likewise water that plays the leading part in determining the creation 

 of plant-communities and their distribution over the soil. 



It is quite true that the special attributes of a habitat result from the 

 co-operation of the most diverse factors, edaphic and climatic, not one 

 of which can be omitted without modifying those special attributes and 

 consequently the vegetation. For instance, vegetation is greatly affected 

 by fertility of the soil, and on a sterile soil there occur only communities 

 of feeble productive power .^ But it is beyond doubt that water occupied 

 the foremost position as a factor bringing about the greatest distinctions 

 in vegetation and structure. We may say : 



The supply of water to the plant and the regulation of transpiration 

 are the factors that evoke the greatest differences in plant-form and plant-life. 



In this connexion we at once meet with two extremes : 



There are many plants that pass the whole or the greater part of their 



^ Page 12. * See Chaps. VII, VIII, XII. 



* Grabner (1898, 1901, 1908), indeed, would have it that nutriment in the soil 

 is the paramount factor. 



