342 
The Ohio Naturalist. 
[Vol. V, No. 7, 
Thus in the history of species as well as in the history of 
individuals, the simple leaf is the first to appear and may usually 
be regarded as the more primitive form. Although the acquire- 
ment of compound leaf forms is a higher development it is not 
necessarily restricted to the higher groups. Some of the best 
types of such forms are found in the lowest leaf bearing plants 
like ferns, cycads and buttercups and are nearly absent in the 
Compositae. They seem to have been acquired independently 
as a parallel development as is shown by their presence in widely 
separated groups and in isolated genera and species. In some 
families as in Leguminosae, Juglandaceae and Umbelliferae, the 
character is already fixed; in others as in Ramxnculus, Geum, and 
Potentilla, it seems to be a more recent development ; while 
others again show no indications whatever of a tendency to 
develop higher types of leaves. 
Before concluding a few words might be said on the advantage 
accruing to plants which possess a higher type of foliage. Plants 
which grow in the shade and where vegetation is dense could 
present a greater surface without additional shading. It would 
obviate the necessity of lengthening the petioles of the lower 
leaves or of decreasing the size of upper leaves and would thus 
be a distinct gain to the plant. This arrangement is especially 
marked in some of the climbers. In ferns which are plants usu- 
ally growing in the shade, a compound leaf seems almost a 
necessity as the stems are as a rule underground and they must 
depend entirely upon their leaves for exposure to air and light. 
Plants which grow in exposed situations would be greatly bene- 
fitted as they could increase their foliage surface enormously 
without exposing themselves to injury by wind, rain or hail. 
This would be most likely to occur in trees. In our common 
Kentucky coffee tree the leaf stalk has taken the place of the 
smaller twigs and its branches present a very naked condition 
in winter, causing them to expose but a small surface to winter 
storms. This would certainly be of great advantage to the tree. 
It seems as though no definite conclusion could be drawn as 
to when, where and why plants develop a more complex leaf 
system, especially as so many plants develop it in connection 
with some of the other features that enable it to reach the light. 
A closer study of the question seems to present more problems 
than solutions. This is undoubtedly because plants are con- 
tinually shifting from place to place and from one condition into 
another. So that if certain characters are developed and become 
fixed when the plant lives in one condition they need not be lost 
if the plant is forced to migrate or if this condition is changed, as 
they might not necessarily be a disadvantage to it. Until then, 
the entire geological history of the different groups is known it 
would be impossible to tell why plants with similar habits and 
