26 



C O N TR I B U T I O N S TO PAL^ONTOLOGY 



the Goshen flora was subtropical is in close agreement with their inferences based 

 on the modern distribution of related species. 



The results of the analysis of leaf characters of the dicotyledons in the Medi- 

 cine Bow floras are shown in table 2. Also introduced in this table are the analyses 



Table 2 — Leaf charactcrs of dicntyledms, showing relative percentages in each category 



of the Goshen flora, the Bridge Creek flora, the modern flora of the Muir Woods, 

 Cahfornia, the modern Panama flora,^ the Eocene WeaverviUe flora of Cahfornia,^ 

 and the Upper Cretaceous Laramie flora of Colorado. 



In compiling table 2, I have used a somewhat different arrangement from 

 that of Chaney and Sanborn, and of MacGinitie. The characters of margin, length, 

 and nervation are placed in the first three columns, as they are considered more 

 reliable and more diagnostic than the remaining characters. There are two reasons 

 for so considering them: (1) these characters have been tested more fuUy in modern 

 forests, chiefly by Bailey and Sinnott; (2) they are more readily and more accu- 

 rately determinable in fossil leaves than are the remaining characters. A quan- 

 titative determination of texture in fossil leaves is somewhat more difficult, since 

 it involves a considerable amount of personal opinion. Likewise in organization, 

 it is often impossible to ascertain whether a fossil leaf is actually a simple leaf or 

 a leaflet of a compound leaf. It is usually necessary in this category to resort to 

 comparisons of the fossil leaves with modern correlatives, a procedure which com- 

 pletely defeats the purpose of this study, namely to make climatic inferences which 

 shall check and supplement the inferences made on the basis of taxonomy and 

 modern distribution of correlatives. The presence or absence of dripping point 

 has not yet been statistically studied in a sufficient number of modcrn forests to 

 be rehably used. It has been my experience, moreover, that it is often a matter 

 of opinion as to just how abrupt and elongate a leaf tip must be to be considered 

 a dripping point. I have also been forced to consider dripping points absent from 

 many fossil leaf species merely because the tip was not preserved, a condition which 

 actually may have resulted from the very presence of a fragile, easily destroyed 

 dripping point. 



' Chaney and Sanborn, ibid., 19-21. 



2 MacGinitie, H. D., Carnegie Inst. Waah. Pub. No. 465, 113, 1937. 



