INVESTIGATIONS ON THE PHYLOGENY OF THE ANGIOSPERMS 1 9 
also frequently trifasciculate. The cotyledon and early leaves in 
several families of Monocotyledons have been shown by Chrysler^^ 
and Coulter and Land^^ to have three bundles (fig. 79), apparently a 
vestige of the more ancient condition. The conspicuous tendency for 
the cotyledonary veins in the seed-leaves of many Dicotyledons to 
unite at the tip of the lamina (figs. 21, 27, 28, 38, and 44) producing a 
closed venation like that of the Monocotyledons, suggests either that 
the Monocotyledons are the more ancient of the two classes, a con- 
clusion opposed by too much evidence from other sources; or that the 
leaf in these plants has been developed by a process of reduction 
much like that gone through by the cotyledons of Dicotyledons and 
by the mature leaves of certain members of that class. The Mono- 
cotyledons apparently had their origin from a palmate dicotyledonous 
stock, ver}^ likely at an early period when the palmate leaf was pre- 
dominant among all Angiosperms. 
Summary 
1. The primitive Angiosperm leaf was palmate in type, probably 
lobed, and was provided with three main bundles which arose separ- 
ately at the node. 
2. This conclusion is based on evidence from palaeobotany, that 
the palmate leaf was more frequent in the Cretaceous and Tertiary 
than at present; from morphology, that there is a correlation between 
the palmate leaf and the multilacunar node and between the pinnate 
leaf and the unilacunar node and that the former nodal type is the 
more ancient, that cotyledons and floral leaves are much more fre- 
quently palmate than are vegetative ones, and that vigorous growth 
emphasizes the palmate type; and from phylogeny, that palmate 
leaves are most frequent in relatively primitive groups and pinnate 
leaves in more advanced ones. 
3. Transitions from the palmate lobed type to all other leaf forms 
may readily be traced. 
4. The chief factor in the evolution of the now dominant pinnate 
leaf seems to have been the development of the petiole, in which 
" The Development of the Central Cyhnder of the Araceae and Liliaceae, 
Chrysler, M. A., Bot. Gaz. 38: 161-184. 1904. 
12 The Origin of Monocotyledony, Coulter, J. M. and Land, W. J. G., Bot. Gaz. 
57: 509-519- 1914- 
