Allard —119— Length of Day in the Past 



conditions of warmth could prevail either with great variations in length- 

 of day, or be accompanied by conditions of a constant length of day such 

 as now prevails only at or near the equator. The resultant effects upon 

 the flora would be vastly different in the two instances. With no latitudinal 

 differentiations in length of day, the two great controlling factors of cli- 

 mate, temperature and daily light duration, would work concomitantly 

 toward a high floristic uniformity over all the earth, and no other combina- 

 tion of these major climatic conditions would operate so efficiently in pro- 

 moting indiscriminate intermingling of dissimilar floristic elements every- 

 where. 



There are few botanists today who have not been impressed with the 

 length-of-day responses of plants. The recognition of this principle of 

 plant response has led to a far greater interest in plant life, its behavior 

 and distributions, than has perhaps ever been shown before, and a wealth 

 of new information has accrued relating to the climatic relations both of 

 our cultivated forms and of the wild forms everywhere. 



It is thought that these speculations concerning the origins and the great 

 changes which may have taken place in some of the ancient floras, will be 

 of some interest to botanists, more especially since the hitherto unrecog- 

 nized but powerfully operative factor of climate, length of day as a 

 differential influence, has been given consideration. 



References: — 



Allahd, H. a., Response of the Woody Plants Hibiscus Syriacus, Malvaviscus Coniattii and 

 Bmtgainvillea glabra to Length of Day. Jour. Agr. Res. 51 (1), 1935. — Allard, H. A., Complete 

 or Partial Inhibition of Flowering in Certain Plants When Days are Too Short or Too Long. Jour. 

 Agr. Res. 57 (10), 1938. — Allard, H. A. and Zaumeyer, W. J., Response of Beans iPhaseolus) 

 and Other l.egumes to Length of Day. Tech. Bull. No. 867. U. S. Dept. of Agric, 24 pp., 1944. — 

 Berry, E. W., The Upper Cretaceous and Eocene Floras of South Carolina and Georgia. U. S. 

 Geol. Survey, Prof. Paper 84, 1914.— Berry, E. W., The Lower Eocene Floras of South-Eastern 

 North America. U. S. Geol. Survey, Prof. Paper 91, 1916. — Berry, E. W., The Upper Cretaceous 

 Floras of the Eastern Gulf Region. U. S. Geol. Survey, Prof. Paper 112, 1919. — Berry, E. W., 

 The Middle and Upper Eocene Floras of South-Eastern North America. U. S. Geol. Survey, Prof. 

 Paper 152, 1924.— Bews, J. W., The Growth Forms of Natal Plants. Trans. Roy. Soc. of South 

 Africa, 5, 1916. — Bews, J. W., Researches on the Vegetation of Natal. Series I, Union of South 

 Africa, Bot. Survey, Mem. No. 5, 1923. — Bews, J. W., Plant Forms and their Evolution in South 

 Africa. London, 1925. — Bews, J. W., Researches on the Vegetation of Natal. Series II, Union 

 of South Africa Bot. Survey, Mem. No. 8, 1926. — Bews, J. W., Studies in the Ecological Evolu- 

 tion of the Angiosperms. New Phytologist 36, Ch. I, pp. 1-21; Ch. II, pp. 65-84- Ch III pp 129- 

 148; Ch. IV, pp. 209-231; Ch. V, pp. 232-248; Ch. VI, pp. 273-294, 1927.— Croll, J., Climate and 

 Time in their Geological Relations. London, 1875. — Croll, J., Discussions on Climate and Cos- 

 mology. London. (Eccentricity of Earth's Orbit), 1889. — Garner, W. W. and Allard, H. A., 

 Effect of Relative Length of Day and Night and Other Factors of the Environment on Growth and 

 Reproduction in Plants. Jour. Agr. Res., 18 (11), 1920.— Jolv, J., Radioactivity and the Surface 

 History of the Earth, Oxford, 1924. — Koppen, Wladimir Peter and A. Wegener, Die Klimate 

 der Geologischen Vorzeit. Berlin, 1924. — Sinnott, Edward W. and Bailey, Irving W In- 

 vestigations of the Phylogeny of the Angiosperms, No. 4. The Origin and Dispersal of Herbaceous 

 Angiosperms. Ann. Bot. 28 (112): 547-600, 1914. — Wegener, A., Die Entstehung der Continente 

 und Ozeane. Die Wissenschaft, Braunschweig, 66, 1920 (Eng. Ed. 1924). 



