AMERICAN 
JOURNAL OF BOTANY 
Vol. II January, 1915 No. 1 
INVESTIGATIONS ON THE PHYLOGENY OF THE 
ANGIOSPERMS 
5. Foliar Evidence as to the Ancestry and Early Climatic 
Environment of the Angiosperms 
Edmund W. Sinnott and Irving W. Bailey 
The leaf of the Angiosperms is so variable in its shape and vena- 
tion among closely related species and so easily modified by environ- 
mental influences that gross foliar characters have been largely 
neglected by the taxonomist and the phylogenist except within small 
groups of plants. A careful survey of evidence obtained from the 
various botanical fields, however, apparently makes possible a recon- 
struction of the primitive Angiosperm leaf with a reasonable degree 
of certainty, and a determination of some of the factors which have 
modified it; and thus suggests not alone the probable ancestry of the 
Angiosperms but also the climatic conditions under which they first 
appeared. The presentation of evidence on which such an hypothesis 
may be built is the purpose of the present paper. 
It is with the more ancient of the two Angiosperm classes, the 
Dicotyledons, that the problem necessarily rests. The two main 
types of leaf venation in this group are the palmate and the pinnate, 
between which intermediate conditions frequently occur. Leaf shape 
is, of course, generally correlated with venation although there are 
numerous instances where broad leaves are pinnate and narrow ones 
palmate. The main leaf types, having reference both to venation 
and shape, may be roughly designated as the palmate simple (fig. 2), 
[The Journal for December (1 : 499-550) was issued 29 Dec. 1914.] 
