ITS THEORKTICAL STRUCTURE. 231 



type, only differing in their special development. And it may 

 be added, that in an early stage of development they all appear 

 nearly alike. That which, under the ordinary laws of vegetation, 

 would have developed as a leafy branch, here developes as a flower ; 

 its several organs appearing under fonus, some of them slightly, and 

 others extremely, different in aspect and in office from the foliage. 

 But they all have a common nature and a common origin, or, in 

 other words, are homologous parts ( 424). 



434. Now, as we have no general name to comprehend all those 

 organs which, as foliage, bud-scales, bracts, sepals, petals, stamens, 

 &c., successively spring from the ascending axis or stem, having ascer- 

 tained their essential identity, we naturally take some one of them 

 as the type, and view the others as modifications or metamorphoses 

 of it. Tlie leaf is the form which earliest appears, and is the most 

 general of all the organs of the vegetable ; it is the form which is 

 indispensable to normal vegetation, since in it, as we have seen, as- 

 similation is effected, and all organic matter is produced ; it is the 

 form into which all the floral organs may sometimes be traced back 

 by numerous gradations, and to which they are liable to revert ivhen 

 flowering is disturbed and the vegetative forces again prevail. 

 Hence the leaf may be properly assumed as the type or pattern, to 

 which all the others are to be referred. When, therefore, the floral 

 organs are called modified or metamorphosed leaves, it is Jiot to be 

 supposed that a petal has ever actually been a green leaf, and has 

 subsequently assumed a more delicate texture and hue, or that sta- 

 mens and pistils have previously existed in the state of foliage ; but 

 only that what is fundamentally one and the same organ develops, 

 in the progressive evolution of the plant, under each or any of 

 these various forms. When the individual organ has developed, its 

 destiny is fixed. 



435. The theory of vegetable morphology may be expressed in 

 other and more hypothetical or transcendental forms. We have 

 preferred to enunciate it in the simplest and most general terms. 

 But, under whatever particular formula expressed, its adoption has 

 not only greatly simplified, but has thrown a flood of light over the 

 whole of Structural Botany, and has consequently placed the whole 

 logic of Systematic Botany upon a new and pliilosophical basis. 

 Our restricted limits will not allow us to trace its historical develop- 

 ment. Suffice it to say, that the idea of the essential identity of the 

 floral organs and the leaves was distinctly propounded by Lin- 



