THE MORPHOLOGICAL COMPOSITION OF PLANTS. 45 



appendages of the axis are homologues : they are all modified 

 leaves. 



Wolff established, and Goethe further illustrated, another 

 general law of structure in flowering plants. Each leaf 

 commonly contains in its axil a bud, similar in structure to 

 the terminal bud. This axillary bud may remain unde- 

 veloped; or it may develop into a lateral shoot like the 

 main shoot; or it may develop into a flower. If a shoot 

 bearing lateral flowers be examined, it will be found that the 

 internode, or space which separates each leaf with its axillary 

 flower from the leaf and axillary flower above it, becomes 

 gradually less towards the upper end of the shoot. In some 

 plants, as in the fox-glove, the internodes constitute a 

 regularly-diminishing series. In other plants, the series they 

 form suddenly begins to diminish so rapidly, as to bring the 

 flowers into a short spike : instance the common orchis. And 

 again, by still more sudden dwarfing of the internodes, the 

 flowers are brought into a cluster; as they are in the cow- 

 slip. On contemplating a clover flower, in which this 

 clustering has been carried so far as to produce a com- 

 pact head; and on considering what must happen if, by a 

 further arrest of axial development, the foot-stalks of the 

 florets disappear; it will be seen that there must result a 

 crowd of flowers, seated close together on the end of the axis. 

 And if, at the same time, the internodes of the upper stem- 

 leaves also remain undeveloped, these stem-leaves will be 

 grouped into a common involucre: we shall have a composite 

 flower, such as the thistle. Hence, to modifications in the 

 developments of foliar organs, have to be added modifications 

 in the developments of axial organs. Comparisons disclose 

 the gradations through which axes, like their appendages, 

 pass into all varieties of size, proportion, and structure. And 

 we learn that the occurrence of these two kinds of metamor- 

 phosis, in all conceivable degrees and combinations, furnishes 

 us with a proximate interpretation of morphological com- 

 position in Phaenogams. 



