Jvm 4, 1915] 



SCIENCE 



833 



Mesophytic-cold-t 



Entire, 

 Per Cent. 



Tiees 10 



Shrubs 14 



Woody 13 



Moist-lowland-tropical 

 Entire, 

 Per Cent. 



Trees 90 



Shrubs 87 



Woody 88 



Nnr-entire, 

 Par Cent. 



Non-entire, 



Per Cent. 



10 



13 



12 



From this table it is clear that leaves with 

 non-entire margins are of very infrequent 

 occurrence in lowland tropical floras, and those 

 with entire margins in mesophytic cold-tem- 

 perate ones. In fact the correlation between 

 leaf structure and climate is so intimate in 

 widely separated regions of the earth and in 

 the distribution of many families, genera and 

 even species that the modifying influences of 

 environment are clearly demonstrated. For 

 more detailed evidence, in regard to correla- 

 tions between foliar structures and climate and 

 the probable function of the non-entire leaf 

 margin, the reader is referred to the following 

 papers.^ 



It has been stated above that in moist trop- 

 ical regions the leaves are of comparatively 

 large size (megaphyllous). Any large hetero- 

 geneous tropical region will contain in conse- 

 quence, among its entire-leaved plants, vary- 

 ing proportions of megaphyllous and micro- 

 phyllous types. Similarly, in sub-tropical and 

 warm-temperate zones the entire leaves will 

 consist of varying proportions of these two 

 tjrpes, depending upon the distibution of rain- 

 fall and other factors. In cold-temperate re- 

 gions, however, the entire-leaves will be com- 

 posed almost entirely of comparatively small- 

 leaved types. 



The percentages of entire-leaved woody 



2 Sinnott, E. W., and Bailey, I. W., "Foliar Evi- 

 dence as to the Ancestry and Early Climatic En- 

 vironment of the Angiosperms, " Am. Jour. Bot., 

 Vol. II., No. 1, January, 1915; Bailey, I. W., and 

 Sinnott, E. W., "The Climatic Distribution and 

 Physiological Significance of Certain Types of 

 Angiosperm Leaf -margin. " Ined. 



Dicotyledonous plants in a few Cretaceous and 

 Tertiary floras are recorded in the next table. 



Tertiary 



Entire, 

 Per Cent. 



Eocene-Green Eiver-Lesq 29 



Eocene-Arctic-Heer 29 



Eoeene-Spitzbergen-Heer 46 



Eocene-Bad Lands-Lesq 29 



Cretaceous 



Entire, 

 Per Cent. 



Montana-Knowlton 62 



Patoot-Arctic-Heer 51 



Atane-Arctic-Heer 81 



Amboy-Newberry 67 



Dakota-Lesq 54 



Earitan-Berry 71 



A comparison of the Tertiary percentages 

 with those of modern floras indicates very 

 clearly the general temperate character of the 

 climates which prevailed in the regions where 

 these fossil floras existed. Similarly, the per- 

 centages of non-entire leaves in the Patoot, 

 Dakota and Amboy Cretaceous formations 

 denote climatic conditions intermediate be- 

 tween those of tropical and temperate regions. 

 The high percentages of entire-leaved forms 

 (megaphyllous) in the Atane beds points to 

 the tropical character of the climate which 

 existed in certain arctic regions during parts 

 of the Cretaceous. 



Of course caution is needed in comparing 

 any specific percentage in this table with that 

 of a corresponding one in the table of living 

 floras. This is due to the fact that one can 

 not always be certain that any known fossil 

 flora is a fair sample of the total ancient vege- 

 tation of which it once formed a part. Fur- 

 thermore, the percentages of entire leaves in 

 fossil and living floras must be homologous, 

 that is, composed of similar portions of mega- 

 phyllous and microphyllous tj^pes. 



In conclusion it should be noted that this 

 method of studying fossil floras rests upon a 

 physiological and ecological basis rather than 

 upon the usual phylogenetic one. It promises 

 to afford a simple and rapid means of gauging 

 the general climatic conditions of the Creta- 



