218 MORPHOLOGY OF THE ANGIOSPERMS 



have. If a carpel be considered an axis, it would be a hollow structure 

 containing other axes, the placenta and its branches, the ovules. 



The claim of homology of carpel and axis fails to explain the existence 

 of open carpels and the ontogenetic closing of carpel primordia. It com- 

 pletely disregards anatomical structure and ontogeny, and is valueless 

 in morphological interpretations. 



When evidence from all fields is considered, none of the twentieth- 

 century concepts of the nature of the carpel can displace the classical 

 view that the carpel is a fertile lateral appendage of a determinate 

 stem tip. In details of position and origin on the stem, and of ontogeny 

 and anatomy, it is like the leaf and is clearly of leaf rank. Comparative 

 studies of the stamens of primitive dicotyledons show that this sporo- 

 phyll, although much more modified than the carpel, is, like the carpel, 

 basically leaflike in form, structure, and ontogeny. The similarity be- 

 tween the two types of sporophylls strengthens the classical view. 



Axial Nature of the Carpel. Interpretations of the sporophylls as 

 branches of the axis, not appendages, take various forms. The simplest 

 of these considers the flower a branching stem. The sporophylls are seen 

 as lateral branches. These are subtended by bracts, the sepals and petals. 

 In very few flowers can position of the floral organs — sporophylls radially 

 internal to outer organs — be seen to suggest this relationship. In ana- 

 tomical structure, all the organs are leaflike, and their vascular traces are 

 like those of leaves, not branches. 



The concept that the carpel is an aggregate of telomes — basic elements 

 of an ancient, ancestral thalloid body — can perhaps be considered an 

 "axial" theory. The carpel, so interpreted, is made up of a determinate, 

 much-branched lateral part of the body; the distal branchlets, fused, 

 form a laminar structure. If the plant body of the angiosperms is in- 

 terpreted in terms of telomes, the carpel can well be so described. Con- 

 sideration of the primitive plant body as made up of basic units, tel- 

 omes, is doubtless of value for the understanding of the more primitive 

 taxa, but its value in the interpretation of the higher taxa, where axis 

 and appendages have become established as morphological units, is 

 doubtful. 



The Sui Generis Theory. Akin to the theory that carpels and stamens 

 do not exist as morphological units is the concept that the sporophylls 

 are "organs sui generis," in other words, organs neither homologues of 

 leaves nor leaflike in nature. The basis for this interpretation was found 

 in supposedly fundamental differences in the structure and behaviour of 

 the apical meristems of reproductive and vegetative stems. The floral 

 apex is considered limited by the development of the carpel, which is 

 described as terminal; proliferation of the apex does not occur. The 



