ITS TIIKOTIKTICAT. STRUCTURE. 225 



are at least analogous to branches, and the leaves of the flower are 

 analogous to ordinary leaves. 



424. But the question which now arises is, whether the leaves of 

 the stem and the leaves and the more peculiar organs of the flower 

 are not homologous parts, that is, parts of the same fundamental 

 nature, although developed in different shapes that they may sub- 

 serve different offices in the vegetable economy ; — just as the arm 

 of man, the fore-leg of quadrupeds, the wing-like fore-leg of the bat, 

 the true wing of birds, and even the pectoral fin of fishes, all repre- 

 sent one and the same organ, although developed under widely dif- 

 ferent forms and subservient to more or less different ends. The 

 plant continues for a considerable time to produce buds which de- 

 velop into branches. At length it produces buds which expand into 

 blossoms. Is there an entirely new system introduced when flowers 

 appear ? Are the blossoms formed upon such a different plan, that 

 the general laws of vegetation, which have sufficed for the interpre- 

 tation of all the phenomena up to the inflorescence, are to afford no 

 further clew ? Or, on the contrary, now that peculiar results are to 

 be attained, are the simple and plastic organs of vegetation — the 

 stem and leaves — developed in new and peculiar forms for the ac- 

 complishment of these new ends ? The latter, doubtless, is the cor- 

 rect view. The plant does not produce essentially new kinds of 

 organs to fulfil the new conditions, but adopts and adapts the old. 

 Notwithstanding these new conditions and the successively increas- 

 ing difference in appearance, the fundamental laws of vegetation 

 may be traced from the leafy branch into and through the flower. 

 That is, the parts of the blossom are homologous with leaves, are 

 leaves in other forms than that of foliage. 



425. The student will have observed, that in vegetation no new 

 organs are introduced to fulfil any particular condition, but the com- 

 mon elements, the root, stem, and leaves, are developed in peculiar 

 and fitting forms to subserve each special purpose. Thus, the same 

 organ which constitutes the stem of an herb, or the trunk of a tree, 

 we recognize in the trailing vine, or the twiner, spirally climbing 

 other stems, in the straw of Wheat and other Grasses, in the colum- 

 nar trunk of the Palm, in the flattened and jointed Opuntia, or 

 Prickly Pear, and in the rounded, lump-like body of the Melon- 

 Cactus. So, also, branches harden into spines in the Thorn, or, by 

 an opposite change, become flexible and attenuated tendrils in the 

 Vine, and runners in the Strawberry ; or, when developed under 



