INVESTIGATIONS ON THE PHYLOGENY OF THE ANGIOSPERMS 9 
such problem as the present one. A general survey of seed-leaf 
characters throughout the Dicotyledons, such as may conveniently 
be found in Lubbock's treatise on seedlings,^ reveals the striking 
fact that the cotyledonary venation in the majority of cases is palmate, 
very often with three main veins. Not only are palmate cotyledons 
present in practically all palmate-leaved species but they occur (and 
often predominate) in every important pinnate-leaved family, as 
well. Some typical cases from all of the great Dicotyledonous orders 
are illustrated in figures 37 to 69. 
The fact that the cotyledon is often broader in proportion to its 
length than is the vegetative leaf cannot explain its predominant 
palmate venation for it will be noted that in Acer, Antigonon, Rhus 
and many others the seed leaf is much narrower, proportionally, than 
the vegetative one but is nevertheless provided with three or more 
palmate veins. Nor can the palmate condition be explained as a 
physiological necessity for all seedlings, for there are numerous 
instances where the cotyledon is pinnate in venation. Taken in con- 
nection with the primitiveness of the trilacunar node, this prevalence 
of three-veined palmate cotyledons among Dicotyledons of all families 
must be regarded as important evidence that the palmate, three- 
veined leaf is indeed the most ancient type for the group. Should 
such a conclusion be clearly established, this preponderance of palmate 
venation in the embryo will evidently furnish an important instance 
of the persistence of an ancient character in plant ontogeny and will 
strongly support the theory of recapitulation in its application to 
the Angiosperms. 
A somewhat similar phenomenon is provided by the peltate leaves 
of Tropaeolum (fig. 71), Hydrocotyle and other plants, where the 
early developmental stages are strongly palmate lobed (fig. 70). 
That this embryonic condition is ancestral for these species is indi- 
cated by its prevalence among closely related forms. 
4. Reversions. — ^There are numerous cases among plants where 
very vigorous growth brings about a reversion to a primitive character 
or intensifies its ordinary development, and it might therefore be 
expected that large and vigorous leaves would tend to revert to a more 
ancient type. In most cases there is little difference in venation 
among the leaves of a single plant, but numerous exceptions do occur 
where the largest and rankest leaves are palmate lobed whereas the 
^ A Contribution to our Knowledge of Seedlings, Lubbock, J. 
