300 THE STRUCTURE OF FLOWERS. 



apetaloas or to have a corolla consisting of a few petals only, 

 it is due to the fact that the petals which are wanting are 

 really present, but have become calycine. 



Origin of Homology. — Though we cannot penetrate into 

 the arcana of life, nor trace the workings of its forces which 

 bring about the development of any organ whatever, I 

 think we can at least reach the physiological starting-point, 

 so to say, of all these changes which I have briefly described. 

 I have already mentioned that we may consider a vascular 

 cord as the fundamental "floral unit," and as all cords are 

 identical in character as long as they are within a pedicel, 

 and, as far as one can observe, identical also in character 

 even when they have penetrated the different organs, we at 

 once see that there is a common source for each and all. 

 Secondly, w^hen we trace these cords from the receptacle or 

 axis into the floral members, we soon discover that any cord 

 can supply two, three, or more totally different organs with 

 their respective branches, as in the case of Campanula 

 medium described above (p. 43). Indeed, starting, say, with 

 five cords in a pedicel, they can supply any number of organs 

 ad libitum, however diverse in character and however 

 numerous they may be. Hence, although normally each 

 whorl is stamped with its own individuality, it is easy to 

 imagine, in accordance with the principles of evolution, that 

 others may partake of it ; and so the characteristic features 

 peculiar to one w^horl can transcend its limits, and influence 

 others as well. 



Beyond some such interpretation as this, I do not think 

 it is possible to go. 



In saying that a fibro- vascular cord can "give rise" to a 

 sepal, or petal, or other organ, I need hardly remind the 

 reader that I am only speaking metaphorically, in describing 

 what one observes in studying the anatomy of flowers. 



