1870.] THEORY OF THE LEAF. 345 



of the Bryophyllum. Indeed, every leaf is a modified branch, and 

 its toothed or serrated edges correspond with the nodes of the 

 stem. 



Further, all the appendages borne on the stem — such as scales, 

 leaves, bracts, flowers, and fruit — are modifications of this one com- 

 mon type. Flowers, the glory of the vegetable world, are merely 

 leaves, arranged so as to protect the vital organs within them, and 

 coloured so as to attract insects to scatter the fertilising pollen, and 

 to reflect and absorb the light and heat of the sun for ripening the 

 seed. Stamens and pistils may be converted, by the skill of the 

 gardener, into petals, and the blossoms so produced are called double 

 — necessarily barren. The Wild Rose has only a single corolla. Cul- 

 tivated in rich soil, its yellow stamens are changed into the blush 

 leaves of the full-blown Cabbage-Rose. There is a monstrosity to 

 which the Garden Rose is liable — the stamens and pistils are converted 

 into green leaves, and the plant begins to develop stem and foliage 

 from the bosom of the petals, just as though the blossom were not 

 the culminating point, but merely a stage in its growth. We see 

 the whole gradual process in the metamorphosis of the common leaf 

 into all the floral organs most beautifully displayed in the normal 

 flower of the common Water-Lily — the outermost circle of petals is 

 greenish, approaching the herbaceous texture and colour of the calyx ; 

 the next circles are purer and more succulent ; and the innermost ones 

 are snowy white, entirely cellular, and, strange to say, begin to show 

 rudiments of an anther at their points. Gradually the petals be- 

 come smaller and narrower, while the anthers on their summits 

 become more distinct, until at length the usual thread-like filaments 

 and golden dusty anthers of perfect stamens appear in the heart 

 of the flower. 



We come next to the fruit, which, in all its astonishing varieties of 

 texture, colour, and shape, is also a modified leaf ; and it is one of the 

 most interesting studies in natural history to trace the correspondence 

 between the different parts of structures so greatly altered and the 

 original type. In the Peach, for instance, the stone is the upper skin 

 of a leaf hardened so as to protect the kernel or seed ; the pulp is 

 the cellular tissue of a leaf expanded and endowed with nutritive 

 properties for the sustenance of the embryo plant ; and the beauti- 

 ful downy skin on the outside is the lower cuticle of the leaf, with 

 the sun -bloom upon it, the hollow l^ne on one side of the fruit 

 marking the union between the two edges of the leaf. So also in 

 the Apple — the parchment -like cover is the upper surface of the 

 leaf, and the flesh is the cellular tissue greatly swollen. In the 

 Orange, the juicy lips enclosing the seeds are the different sections 



