Traces of Unity in Plants. 1 5 



compound in the water, and the former or latter kind 

 is developed as the level of the water happens to fall or 

 rise. And the petiole, or leaf-stalk, which in its ordinary 

 form is obviously a modification of the node which 

 enters into the formation of the branch or stem, is as 

 obviously connected with the leaf-blade by the excep- 

 tional forms which are presented in the orange tree, in 

 the greater number of the acacias of New Holland, and 

 in many other cases forms in which the ordinary stalk- 

 shape is more than half lost in the blade-shape : and so 

 it is that a connection may be traced, not only between 

 simple leaves and compound leaves, but also between 

 the blade of the leaf and the stalk, and between the 

 latter and the node. 



The passage from the leaves to the parts composing 

 the flower is exhibited in many ways. The wreaths 

 called " floral leaves," which frequently enclose the 

 flower, are true leaves, and the involucres of plants, such 

 as the common sun-flower or marygold, are formed of 

 elements between which and the ordinary leaflets every 

 possible gradation may be traced upon the same stalk. 

 Even the common arrangement of the parts of the flower 

 in whorls is not peculiar, for the same plan holds good, 

 not only in the case of floral wreaths and involucres 

 generally, but also in that of many true leaves a case, 

 of which the needle-clusters of the conifers may serve 

 as an example. Indeed, it is almost a matter of chance 

 whether the growth of a plant should declare itself in 

 foliage or flowers, the tendency being leaf-ward if the 

 plant be overfed, flower-ward if the supply of food be 

 stinted. 



Nor is the case of the calyx or corolla in any way 

 peculiar. Ordinarily the petals are gaily tinted, and the 

 sepals are green like the leaves ; but this distinction is 



