142 STRUCTURE AND UNITS OF VEGETATION. 



purpureae pais, etc. The full form once given, Eriophorum-oxodion or Aristida- 

 pois would meet all requirements, except where actual confusion may arise 

 when there are two dominants of the same species in one association or 

 associes. 



The names of units are necessarily long at best, and it seems both desirable 

 and justifiable to shorten them in every legitimate way. The most efficient 

 way of doing this is the one already suggested, namely, of using the name of the 

 chief genus or even a characteristic genus alone in the case of formation, asso- 

 ciation and associes, exactly as has been found so successful in the case of 

 families and orders. In the case of terminations in particular there can be no 

 valid objection to the use of shortened stems and of the contraction or elision 

 of successive vowels. The classical purist will find the former method objec- 

 tionable, but the fact remains that it was in use by classical writers themselves. 

 A study (Clements, 1902 : 31) of Greek neuters in -naros, nom. -fiaj e. g., 

 sperma, stoma, etc., has shown that some of them occur usually in this form, 

 and still more take this form frequently. In their use in biology, Greek and 

 Latin must be regarded as living languages and hence subject to change 

 along the lines already indicated. Hence there is the warrant of brevity and 

 convenience as well as of actual classical practice for the shortened forms found 

 in Spermophyta, Dermocybe, stomal, etc. This usage may well be extended to 

 other imparisyllabic stems in -idis, -itis, etc. Thus Calamgrostidetum would 

 become Calamngrostetum; Heleocharitetum, Heleocharetum; Lychnidetum, 

 Lychnetum. Such abbreviations have already been made, though it is very 

 doubtful whether such extreme cases as the shorterning of Pdkim,ogetonetum 

 to Potamstum are to be approved. The contraction or elision of vowels 

 especially is often desirable also, even though the gain is small. The chief 

 gain is in pronunciation rather than in spelling, as Picetum for Piceetum, 

 Hordetum for Hordeetum, and Spiretum for Spiraeetum. 



Formatioii groups. — The arrangement of formations into higher groups has 

 been based upon various grounds. The first systematic grouping was that of 

 Schouw (1823 : 157), who used the amount and nature of the water-content to 

 establish the four generally accepted groups hydrophyta, m^sophyta, xerophyta, 

 and halophyta, though he named only the first and last. The term xerophyte 

 or xerophilous dates back to Thurmann (1849) and mesophyte to Warming 

 (1895), who adopted Schouw's classification in essence. Drude (1890:37) 

 classified formations as (1) forest, (2) grassland, (3) swamp moor, (4) miscel- 

 laneous, rock, water, and saHne. Pound and Clements (1898 : 94; 1900 : 169) 

 adopted Warming's divisions, but subdivided mesophytes into hylophytes, 

 poophytes, and aletophytes. Schimper (1898), while recognizing water-content 

 groups, classified formations with respect to life-form as forest, grassland, 

 and desert, and with regard to habitat as climatic and edaphic. Graebner 

 (1901 : 25) grouped formations on the basis of soil solutes into those on (1) per- 

 nutrient, (2) enutrient, (3) saline soils. Cowles (1901 : 86) used physiography 

 and development for the basis of the following groups: (A) Inland group: 

 (1) river series, (2) pond-swamp-prairie series. (3) upland series; (B) Coastal 

 group: (1) lake-bluff series, (2) beach-dime-sandhill series. Clements 

 (1902 : 13) arranged formations in various groups, based upon medium, 

 temperatiu-e, water-content, light, soil, physiography, physiognomy, associa- 

 tion, and development. Schroter (1903 : 73) proposed two major groups: 



