THE EVOLUTION OF GROWTH-FORMS 179 



phytes, parasites, and herbaceous shade plants, all of which may 

 occur in primitive habitats along with trees, are probably all much 

 more recent than the trees. Probably all of the angiosperms of 

 desert and semi-desert conditions are relatively recent. Extreme 

 hydrophytes or aquatic plants are also thought to be derivative. 

 The annual type of flowering plant is considered the most recent 



of all. 



REFERENCES 



Bews, J. W.: Plant Forms and Their Evolution in South Africa, London, 



Longmans, Green & Co., 199 p., 1925. 

 Cannon, William Austin: General and Physiological Features of the More 



Arid Portions of Southern Africa With Notes on the Climatic Environment, 



Carnegie Inst. Washington Publ., 354, VIII + 159 p., 31 pi., 13 fig., 1924. 

 Emerson, Fred W.: Subterranean Organs of Bog Plants, Bot. Gaz., 72, 359- 



379, 11 fig., 1921. 

 Maximov, N. a.: The Plant in Relation to Water, London, George Allen & 



Unwin, Ltd., 1929. 

 The Physiological Significance of the Xeromorphic Structure of Plants, 



Jour. EcoL, 19, 273-282, 1931. 

 RiGG, George B.: A Summary of Bog Theories, Plant World, 19, 310-325, 



1916. 

 Comparisons of the Development of Some Sphagnum Bogs of the 



Atlantic Coast, the Interior, and the Pacific Coast, Am. Jour. Bot., 27, 1-14, 



1940. 

 Runyon, E. H.: Ratio of Water Content to Dry Weight in Leaves of the 



Creosote Bush, Bot. Gaz., 97, 518-553, 1936. 

 Shreve, Edith B. : Seasonal Changes in the Water Relations of Desert Plants, 



Ecology, 4, 266-292, fig. 1-11, 1923. 

 Shreve, F.: The Plant Life of the Sonoran Desert, Sci. Monthly, 42, 195-213, 



1936. 

 Skipper, E. G.: The Ecology of the Gorse (Ulex) With Special Reference to 



the Growth-forms on the Hindhead Common, Jour. Ecol., 10, 24-52, pi. 1, 9 



fig., 1922. 

 Smith, William G.: Raunkiaer's "Life-forms" and Statistical Methods, Jour. 



Ecol., 1, 16-26, 1913. 

 Stoddart, L. a.: Osmotic Pressure and Water Content of Prairie Plants, 



Plant Physiol., 10, 661-680, 1935. 

 Wood, J. G.: The Physiology of Xerophytism in Australian Plants, Jour. 



Ecol, 22, 69-87, 1934. 



