12 EDMUND W. SINNOTT AND IRVING W. BAILEY 
the three traces went off pretty directly into the lamina as is shown in 
our reconstruction (fig. 83). 
If the view thus set forth is a sound one we should be able to trace 
the transitional steps between such a primitive leaf and the various 
types of foliage which now occur throughout the Angiosperms. 
Intermediate conditions between the palmate lobed and the pal- 
mate simple are to be found in several genera such as Acer, Rubus, 
Viburnum, Sterculia, Malus and others. In fact, the genus Acer 
(figs. I to 11) shows in its various species all transitions from simple 
pinnate to ternately compound. In many such plastic genera and 
families, of which the Araliaceae are another notable example, almost 
all leaf types may occur in closely related species and it is common to 
find several of them, with all sorts of intermediate conditions, even 
on the same plant. In all such cases vigorous growth emphasizes 
or restores the palmate lobed condition. In such groups as the 
Piperaceae, Melastomaceae and others the lobed condition seems to 
have been entirely lost, although the venation is still palmate. With 
the loss of the lobes the two lateral veins usually curve inward, some- 
times even giving rise to a practically closed venation. 
The palmate compound type has evidently arisen from the lobed 
one simply by an increase in the depth of the sinuses. The various 
steps may often be traced in the same species or even on one indi- 
vidual as in species of Acer (figs. 6 and 7), Rubus, the Araliaceae and 
many others. Since most palmately lobed leaves have three main 
veins, the compound ones derived from them are for the most part 
trifoliate. In many cases each leaflet of a trifoliate compound leaf 
becomes compound, in its turn, thus giving rise to the ternately com- 
pound type (fig. 11). 
The pinnate simple leaf seems to have had its origin from the 
lobed type through the disappearance of the lobes (palmate simple) 
and a great reduction or disappearance of the lateral veins. Number- 
less transitional steps may be found, especially in the more plastic 
genera (figs, i, 2 and 3, 12, 13 and 14). Most families which are 
preponderantly simple pinnate in leaf type have a few species or genera 
where the two basal veins are especially prominent or in which the 
leaf is essentially palmate. In certain cases (Rutaceae and others) 
the simple pinnate leaf probably represents the terminal leaflet of a 
reduced compound leaf. 
The pinnate lobed type has apparently been derived from the 
