66 BASES AND CRITERIA. 



ing is due to the fact that oecology is only in its infancy, and that very few 

 detailed investigations of plant-communities have been conducted, the pub- 

 lished descriptions of vegetation being nearly always one-sided and floristic, 

 as well as very incomplete and unsatisfactory from an oecological stand- 

 point." 



The terms employed are those suggested by Clements (1902 : 5) and 

 adopted by Warming for most of his divisions: 



I. Hydrophytes: Chresard maximum to very high, the soil being water or' covered with 

 water; climate usually moist. 



1. Emophytes: Entire plant submerged; no transpiration or functional stomata. 



2. Plotophytes: Plant floating, at least the leaves; transpiration and functional 



stomata on upper surface of leaves at least. 



3. Helophytes: Amphibious, rooted in water or mud; transpiration high and stomata 



on both surfaces, the stem often functioning as a leaf. 



II. Mesophytes: Chresard medium, soil moist; climate moist; transpiration high to 

 medium. 



4. Heliophytes: Sun-plants, growing in sunlight or light stronger than 0.10. 



5. Sciophytes: Shade-plants, growing in light less than 0.10. 



III. Xerophytes: Chresard low, soil physically or physiologically dry, climate usually dry, 

 or various; transpiration low. 



A. Soil physiologically dry, climate various: 



6. Halophytes : Chresard low, due to an excess of soil salts. 



7. Psychrophytes : Chresard low, due to cold soil or to ice. 



8. Oxyphytes: Chresard low, due to lack of oxygen in the soil. 



B. Soil physically dry, climate various: 



9. Lithophytes: Chresard low, due to a rock matrix. 



10. Psammophytes : Chresard low, due to sandy or gravelly soil. 



11. Chersophytes: Chresard low, due to a rock substratum. 



C. Climate dry and soil physically dry in consequence: 



12. Eremophytes: desert plants, chresard low or lacking much of the year. 



13. Psilophytes: grassland plants (prairie, plains, steppes), chresard low some of the 



year. 



14. Drymophytes: bushes, shrubs, and small trees, mostly sclerophyll scrub, chaparral, 



and woodland; chresard low or discontinuous. 



The changes from Warming's system lie in the subdivision of hydrophytes 

 and mesophytes, well-recognized distinctions which Warming himself makes 

 use of (18, 165), in the distribution of conifers among helophytes, mesophytes, 

 psammophytes, and drymophytes, in the line drawn between desert and 

 grassland plants, and in treating the bush-shrub form as primary and the 

 division into sclerophyll and deciduous types as secondary. 



Indicator value. — Habitat-forms are the most satisfactory of all indicator- 

 forms. This is chiefly because of their obvious response to the controlling 

 factors which the forester, grazing expert, and others must deal with. This is 

 partly also because they mark out a definite area in which these factors pre- 

 vail. For all practical purposes in a particular region, habitat-forms con- 

 stitute the ground-work of an indicator system. This is evident when it is 

 realized that the fourteen groups comprise all dominants and thus each 

 habitat-form has a community value as well. When reinforced by vegetation- 

 forms in so far as their significance for climate is known, and by ecads and 

 growth-forms for the more recent or the minor effects of physical factors, 

 habitat-forms afford a nearly complete system of indicators for the practical 

 application of biology. It is still necessary to interpret some of them with 



