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, cvcads and buttercups and are nearly absent in the 

 Compositae. They seem to have been acquired independently 

 as a parallel development as is shown b}^ 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 Ranunculus, 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 tlien, 

 the entire geological history of the different gr()U])s is known it 

 would be impossible to tell why plants with similar habits and 



