220 MORPHOLOGY OF THE ANGIOSPERMS 



and inferior ovaries are autonomous structures and bear no phyletic 

 relation to one another. 



Another interpretation of the appendages of the floral meristem is 

 based on the pattern of origin of these organs on the stem apex. Leaves 

 are considered to be produced in helices; the sepals, and sometimes the 

 petals, stand in the same series at the end of the spii-als, but the ar- 

 rangement of stamens and carpels is said not to continue the helices. 

 (No mention is made of the taxa — Nymphaeaceae, Paeoniaceae — in 

 which the sporophylls do continue the spiral series of the perianth.) 

 Leaves are said to be formed by an "annular meristem," a part of the 

 tunica, but, near the apex, the tunica is used up in the formation of 

 the lower sterile appendages, and the corpus alone is involved in the 

 formation of the fertile appendages. The interpretation of the his- 

 tological behavior of the tunica and corpus when the floral organs are 

 being formed is involved and obscure. It appears that, since the sporo- 

 phylls have — in the opinion of the proponent of this theory — an origin 

 entirely different from that of leaves, they are not of leaf rank; appar- 

 ently they are considered as of less than organ rank. By another 

 morphologist, they have been called "lobes of the receptacle." 



The view that floral organs are mere excrescences of the axis and not 

 independent organs can be held only if anatomical structure and early 

 ontogeny are meaningless, and if morphology has no significance. The 

 theories of acarpy "hardly come within the province of morphology," 



The Caytonialian Theory. A Mesozoic group of fossil seed plants, the 

 Caytoniales, provide the basis for another theory of the origin and 

 nature of the carpel. Although the relationships of these plants are un- 

 certain, they have received considerable attention as possible ancestors 

 of the angiosperms, because their ovule-bearing organs have been in- 

 terpreted as representing an early stage in the evolution of the carpel. 

 The Caytonialian megasporophyll is a frondlike, pinnate, dorsiventral 

 organ, consisting of an axis, which bears two lateral rows of globose 

 "cupules," or "ovaries." Each cupule has a median longitudinal vein, 

 along which ovules are borne. A folliclelike carpel is considered derived 

 by the reduction and condensation of this fertile organ; the axis is 

 greatly shortened and the cupules reduced to the lowest member of 

 each row, and these fused to the axis and to each other. In the complex 

 organ so formed, the axis of the ancestral sporophyll would form the 

 midvein of the follicle; the vascular bundles of the two cupules would 

 form the ventral bundles along which the ovules are borne; the ovules 

 of each cupule form one of the two rows. This seems a farfetched and 

 complex derivation for so simple a structure as the follicle. 



Structurally, the carpel and the Caytonialian sporophyll are wholly 

 unlike; the carpel is palmately veined, the Caytonialian organ strongly 



