378 STRUCTURE OF FLOWERING PLANTS. PART n. 



SECTION XII. 



GENERAL STRUCTURE OP FLOWERING PLANTS. 



IN some of the Cryptogamic families fertilization takes 

 place before the plant itself is developed. In the two 

 highest classes, those containing the great groups of 

 Flowering Plants, on the contrary, it is the ultimate re- 

 sult of the inflorescence, which consists of calyx, corolla, 

 stamens, and pistils, all which are the later expansions 

 of the cellular tissues and groups of vessels which have 

 in earlier stages of development formed the leaves. They 

 contain the same materials, and in fact they are leaves 

 modified in form, structure, and function. 



Although the almost innumerable diversities in the 

 form of leaves must produce corresponding diversities 

 in the inflorescence, yet the general characteristics are 

 the same or similar in both of the great botanical classes. 

 The structure of the calyx and corolla which form the 

 floral envelope of the fructification, is similar to that of 

 leaves. The calyx consists, in its early stage, of several 

 parts called sepals, which have all the characters of 

 leaves ; subsequently they are sometimes united by their 

 edges, so as to form a tube, or are otherwise modified. 

 The corolla only differs from a leaf by greater delicacy 

 of organization ; it has fewer stornates or breathing 

 pores, and the veins have less woody fibre and some- 

 times many spiral vessels ; the veins in the petals of 

 chickweed and some other plants are entirely composed 

 of spiral vessels. The calyx and corolla protect the 



