382 



PLANT MORPHOLOGY 



one or more ovules (Fig. 318^). Generally a slender stalk-like style arises 

 from the ovary. In some compound pistils the styles as well as the 

 ovaries are united, while in others the styles are wholly or partly free 

 (Fig. 32G). The style may be hollow but usually is solid. The tip of the 

 style, termed the stigma, is not a morphological unit, but merely an 

 exposed and often expanded portion of the tissue that lines the ovarian 

 cavity and extends upward through the style. In some flowers the stig- 

 matic surface extends down the outside of the style. 



ft 



Fig. 326. Pistils showing various degrees of union between the carpels. A, five separate 

 carpels in the flower of stonecrop (Sedum), X3; B, pistil of garden pink (Dianthiis) with 

 two carpels having united ovaries and free styles, X3; C, pistil of geranium {Pelargonium) 

 with five united carpels having free stylar tips, X6; D, pistil of nightshade (Solanum) with 

 two completely united carpels, X6. 



An ovary may contain a single cavity (locule) or two or more cavities 

 separated from one another by partitions. The ovules may be attached 

 to the walls of the ovary or to the partitions between the locules, in either 

 case being foliar in origin. In some cases the receptacle grows upward 

 into the ovarian cavity and bears the ovules either terminally, laterally, 

 or in both ways. Such ovules are cauline in origin. 



The carpel of angiosperms is generally regarded as the equivalent of an 

 infolded leaf bearing ovules along its fused margins. In fact, in many 

 apocarpous flowers the carpel arises as an open structure that encloses the 

 ovules as development proceeds. Although a foliar organ, the carpel is 

 not a transformed foliage leaf. It is a sporophyll — an organ with its own 

 evolutionary history reaching far back into a pteridophyte ancestry. 

 Sporophylls and foliage leaves have undergone a parallel evolutionary 

 development. Another view regarding the nature of the carpel is that it 

 is a greatly reduced branch system. This theory is based on its supposed 



