INTRODUCTION. 17 



Phanerophytes: Trees and shrubs with buds exposed on branches. 



Chamaephytes: Plants with their dormant buds on the surface of the soil or just 



above it (30 cm.)- 

 Hemicryptophytes : Plants with buds in the surface layer of the soil. 

 Cryptophytes : With subterranean dormant buds. 

 Therophytes: Perennating as seeds; annuals. 



This classification expresses the physiological diversities of the vege- 

 table kingdom in a very inadequate manner. It lays stress upon the 

 resting organs, with total disregard of what we may term the "work- 

 ing organs." 



Its author has more recently^ proposed a subdivision of his group 

 ''phanerophytes," based on the size of the leaves. These six "size- 

 classes" make it possible to use somewhat more definite terms in 

 descriptive plant geography, but they do not satisfy the requirement 

 for a more precise knowledge of the physiological significance of leaf- 

 size. The fact that the transpiring power of leaves is not definitely 

 related to their size is one of the considerations which makes this 

 criterion of doubtful value even for a preliminary classification of 

 growth-forms. 



Raunkiar, Paulsen, and other workers have used the above system 

 of growth-forms to derive what they have designated as "biological 

 spectra." By this method the entire flora of a given region is appor- 

 tioned among the five classes of the system, and the values are thus 

 secured for the percentage of the total flora which is formed by each 

 class. These spectra possess little value to the student of vegetation, 

 inasmuch as they are based upon a consideration of the flora rather 

 than the vegetation. The biological spectrum of a pine forest with 

 175 species of root perennials growing in its shade would be very 

 sUghtly changed by the removal of the pines, although this would 

 effect a very profound change in the character of the vegetation. The 

 securing of the biological spectrum for a given number of the com- 

 monest plants of an area, as has been done by Taylor^ for Long Island, 

 gives results of some value, but their ecological importance is still 

 limited by the inadequacy of the classification. 



The most carefully elaborated system of growth-forms is that of 

 Drude, proposed in his Oekologie der Pflanzen.^ This system is 

 thoroughgoing and complete at the same time that it is eminently 

 natural, in the sense that it comprises almost no subjective or phylo- 

 genetic distinctions. The principal subdivision of the vegetable king- 

 dom is into terrestrial, aquatic, and non-vascular plants, and the total 



'Raunkiar, C, Om Bladstorrelsens Anvendelse i den biologiske Plantegeografi, Bot. Tidsak 

 3.3:225-240, 1916.— Translation by G. D. Fuller and A. L. Bakke in The Plant World 21:25-37, 

 1918. 



*Taj'lor, Norman, Flora of the vicinity of New York, a contribution to plant geography, 

 Mem. New York Bot. Gard., v. vi4-683 p. New York, 1915. 



^Drude, Oscar, Die Okologie der Pflanzen, 308 p., 80 figs., Braunschweig, 1913. 



