THE CARPEL 219 



vegetative axis is unlimited in development, and the leaf is a lateral 

 organ. The leaf arises as a flattened organ; the carpel as a tubular organ; 

 if leaflike, it would be laminar in early stages. The floral apex is broader 

 and flatter than the vegetative apex. 



The structure of many flowers shows that these differences do not 

 exist. The broader apex of the floral stem tip is the result of the close 

 arrangement of the appendages and the cessation of growth in length, 

 and is seen in determinate vegetative stems and in short-shoots and 

 thorns. The carpel is not terminal on the floral apex but lateral, as 

 shown by ontogeny and by vascular anatomy. The axis continues beyond 

 the uppermost carpels in many taxa, as is evident in external form and 

 in vascular structure. The carpel develops like a leaf in every detail, 

 from its origin in the apical meristem to apical and marginal growth 

 of the lamina. The primitive carpel is, in early stages, laminar in form 

 (it closes by the ontogenetic fusion of the margins); only the highly 

 specialized carpel arises as a tubular structure (fusion of the margins 

 is congenital). The sui generis theory is without support from ontogeny 

 or vascular anatomy. 



Theories of "Acarpy." The theory that floral appendages do not exist 

 as morphological units received some attention in the early twentieth 

 century. It has been expressed in two forms, with supporting evidence 

 derived chiefly from ontogeny and physiology. The appendages have 

 been considered mere emergences, determined in position, number, and 

 nature by nutritional and spatial relationships in early stages of stem- 

 apex ontogeny. Vascular structure, under these theories, has no signifi- 

 cance; its form is dependent upon physiological demand; it is not con- 

 servative of ancestral form and has no phyletic significance. 



Under one interpretation, the flower is considered to consist of a 

 determinate stem tip, divided into lower, sterile, and upper, fertile 

 areas. Emergences arising on the lower part are sterile and form bracts 

 and sepals; those on the upper part bear sporogenous tissue and con- 

 stitute the stamens, ovules, placentae, and carpel walls. The lower fer- 

 tile emergences may become sterfle and form petals and staminodia. 

 Above the fertile emergences, other sterile structures, styles and stigmas, 

 appear. The carpel is looked upon as a phyllocladlike, ovule-bearing 

 emergence; the ovules as enclosed by the inrolling of the margins. 



The basis for this understanding of flower structiue is that each floral 

 type is an individual expression of flowering; the comparison of the 

 achene with other fertile emergences need not imply evolutionary de- 

 velopment from ancestral carpels of any type. These statements imply 

 that there is, for the carpel (as for all appendages), no basic plan or 

 form, no natural relationship among types; follicle and achene, superior 



