CRITERIA. 



57 



LIFE-FORMS. 

 History.— The concept of the life-form was first formulated by Humboldt 

 (1805 : 218), who used the term vegetation-form. Under various names, 

 the concept has since been employed by many plant geographers and ecolo- 

 gists, and several have proposed more or less complete systems of classifica- 

 tion. Grisebach (1872), like Humboldt, based vegetation-forms upon physi- 

 ognomy, and both systems have in consequence little more than historical 

 value to-day. Warming (1884) and Reiter (1885) contributed many of the 

 essentials of the modern systems, but these probably owe more to Drude 

 (1890, 1896) than to anyone else. Krause proposed a classification in 1890 

 and Pound and Clements (1898) modified that of Drude somewhat in applying 

 it to American vegetation. For this reason it is proposed to treat the latter 

 here in detail, as well as the more recent systems of Raunkiaer (1903-1907), 

 Warming (1908-1909) and Drude (1913). It will readily be seen that all of 

 these have much in common, though this is not obvious in Raunkiaer's 

 classification, which is based mainly upon adaptation for overwintering. All 

 of them are founded more or less upon the two principles enunciated by Drude, 

 namely, (1) the r61e played by a particular species in vegetation and (2) its 

 life-history under the conditions prevailing in its habitat, with especial 

 reference to duration, protection, and propagation. In the following discus- 

 sion life-form is used as the general term to include vegetation-forms, habitat- 

 forms, growth-forms, etc. 



Pound and Clements, 1898-1900.— As indicated above, the system employed 

 by Pound and Clements in the " Phytogeography of Nebraska" (1898 : 45; 

 1900 : 95; cf. Clements, 1902 : 616) was essentially the earlier system of 

 Drude (1896) modified to fit the vegetation of a prairie State. It possessed 

 some intrinsic interest in that the entire flora of the State was passed in review 

 from the standpoint of the various groups, and with reference to the general 

 conditions of the different habitats (1900 : 95-312). Vegetation-forms were 

 arranged in 7 main groups, which were divided into 34 minor ones. This sys- 

 tem was used by Clements and Clements in "Herbaria Formationum Colora- 

 densium" in 1902 and "Cryptogamae Formationum Coloradensium " in 1906. 



I. Woody plants. 



1. Trees. 



2. Shrubs. 



3. Undershrubs. 



4. Climbers and twiners. 

 11. Half shrubs. 



5. Half shrubs. 



III. Pleiocyclic herbs (perennials). 



6. Rosettes. 



7. Mats. 



8. Succulents. 



9. Creepers and climbers. 

 Turf -builders 



10. Sod-formers. 



11. Bunch-grasses. 

 Rhizomata. 



12. Rootstock plants. 



13. Bulb and tuber plants. 



14. Ferns. 



IV. Hapaxanthous herbs. 



15. Dicyclic herbs (biennials). 



16. Monocyclic herbs (annuals). 



V. Water plants. 



17. Floating plants. 



18. Submerged plants. 



19. Amphibious plants. 

 VI. Hysterophytes. 



20. Saprophytes. 



21. Parasites. 

 VII. Thallophytes. 



22. Mosses. 



23. Liverworts. 



24. Foliaceous lichens. 



25. Fruticulose lichens. 



26. Crustaceous lichens. 

 Fungi. 



27. Geophilous fungi. 



28. Xylophilous fungi. 



29. Biophilous fungi. 



30. Sathrophilous fungi. 



31. Hydrophilous fungi. 



32. Entomophilous fungi. 

 Algae. 



33. Filamentous algae. 



34. Coenobioid algae. 



