VEGETATION-FORMS. 63 



relations introduced by taxonomy and permits a consistent treatment of 

 habitat-forms with their more evident factor correlations. It contains the 

 essentials of the systems discussed above, inasmuch as Drude states that 

 the basic life-forms are trees, shrubs, perennial and annual herbs, Warm- 

 ing divides his group of land-plants into monocarpic and polycarpic, while 

 Raunkiaer's largest groups, phanerophytes, cryptophytes, and therophytes, 

 practically correspond to woody plants, perennial and annual herbs. In 

 giving more or less equal value to the life-period, method of over-wintering, 

 and conservation of shoots and success in competition, it appears desirable to 

 recognize four coordinate groups, viz, annuals, biennials, herbaceous peren- 

 nials, and woody perennials, characterized as follows: 



1. Annuals: Passing the winter or dry season in seed or spore form alone; no propagation 



or accumulation of aerial shoots; living one year. 



2. Biennials: Passing one unfavorable season in the seed or spore form, and the next as a 



propagule; no accumulation of aerial shoots; living two or parts of two years. 



3. Herbaceous perennials: Passing each unfavorable season in both seed or spore and 



propagule form; no accumulation of aerial shoots; living several to many years, 



4. Woody perennials: Passing each unfavorable season as seeds or spores, and aerial shoots 



or masses, often with propagule forms also, especially when injured; living many 

 seasons as a rule. 



Each of these divisions is thoroughgoing and all forms of annual habit are 

 placed in the first group, whether flowering plants, mosses, or fungi, just as 

 perennials are placed in their respective group regardless of their systematic 

 position or habitat-form. The varying nature of the four groups makes it 

 obviously impossible to employ the same criterion for the division into types. 

 For annuals and biennials, the form of the aerial plant body is probably of first 

 importance and the size next, while for woody plants height is perhaps most 

 decisive, leaf-character next, and form last. While perennial herbs usually 

 show the most marked differences in the propagules, the form of the aerial 

 shoot is often even more distinctive, and both criteria must be employed as 

 occasion warrants. The final result is a simple compact system, closely 

 resembling the earlier one of Drude (1896; Pound and Clements, 1900) 

 and different but little in essence from that of Raunkiaer. For the 

 study of indicators only the major divisions appear to be of value at present, 

 and these alone are given in the outline. 



Indicator significance of vegetation-forms. — It is obvious that the vegeta- 

 tion-forms of climax dominants are indicators of climate. This has long been 

 recognized as the basis for the climatic zones of continents and mountains. 

 The same principle applies to climax formations generally; and these are 

 accordingly taken as indicators of the major climates of the globe (Clements, 

 1916). This close correlation between the major vegetation-forms and climate 

 as expressed in progressively favorable conditions of temperature and moisture 

 is paralleled by the succession of vegetation-forms in the development of a 



