INTRODUCTION. 15 



organs, the systems of arrangement of leaves (phyllotaxy), the stelar 

 anatomy of the stem, the existence and character of vestigial structures, 

 and the recapitulation of ancestral features in the early life history 

 of the plant. The facts which fall under these categories have been 

 of long-standing use in phylogenetic classification, but have no direct 

 bearing upon the present relation of the plants to their environmental 

 conditions. Therefore these are not the criteria that would be useful 

 in classifying plants for the purposes of ecology and plant geography. 

 For these purposes we require a classification which shall give first 

 attention to the vegetative rather than the reproductive organs of the 

 plants, and to those features and structures which have to do most 

 obviously with their relation to the conditions of the soil and atmos- 

 phere. 



When plant geographers first began to break away from floristic 

 considerations and commenced to consider plants collectively, as 

 vegetation, they felt the need of a means by which it would be possible 

 to express physiological relationships. It was a very difficult thing 

 to depart from the point of view by which plants could be placed in 

 such definite categories as the Saxifragacese or the Liliaceae, or in such 

 groups as ''arctic circumpolar" or "littoral pantropist." It was still 

 more difficult to attempt, for example, to arrange the plants of heath, 

 moor, tundra, and alpine meadow, in a series of groups that would 

 bring out their physiological affinities. The very instant that we 

 distinguish between the vegetation of any two areas we have taken 

 into account, consciously or unconsciously, certain features of differ- 

 ence between the plants of these areas. We notice the difference 

 between the soft carpet of short grass which lies just above mean high 

 tide in a brackish marsh and the tall, coarse grass which inhabits the 

 quiet shallows below the high-tide line. We notice the difference between 

 the forests of the southern Alleghenies and those of the Gulf Coast. 

 In each case we have had our attention called to certain differences 

 in the gross anatomy of the plants involved. In spite of the fact that 

 the plants which characterize the two areas of marsh are both grasses, 

 we recognize in them plants of different type, just as we distinguish 

 the pines of the Gulf Coast and the oaks and chestnuts of the Alleghen- 

 ian region. It is these obvious differences between plants, conspicuous 

 even to the man who knows no Latin names for them, that form the 

 basis for all the distinctions between vegetational areas. 



Considerable attention has been given, from time to time, to the 

 definition of these anatomically and physiologically distinctive types 

 of plants which are best designated as growth-forms. These attempts 

 have a very fundamental importance to plant geography, for, although 

 many of them have been extremely crude, they represent an attempt 

 to express an ecological similarity that exists between many plants of 

 distant phyletic relationships. They represent an effort to establish 



