VEGE TA TIVE REP ROD UCTION. 



241 



the carpels may be united to form a single compound pistil. 

 This union is commonly brought about (i) by the actual 

 growing together of the parts in a very young stage, so that 

 the cells interlock and become partially or completely united; 

 or (2) the carpels develop, not as separate parts, but as a 

 ring of tissue growing up from the surface of the axis; or, 

 (3), a portion of each carpel develops separately, and later 

 these distinct parts may be lifted by the growth of the ring 

 of tissue beneath them (fig. 249). 



339. The union * of the carpels may be only *at the base ; 

 or it may involve the entire ovulary, leaving the styles free ; 



FIG. 249. FIG. 250. FIG. 251. 



FIG. 249. Pistil of white hellebore (Veratrum album} showing three carpels separate 

 above only. Magnified about 6 diam. After Berg and Schmidt. 



FIG. 250. Calyx and pistil of the manna ash (Fraxinus omits) showing calyx leaves 

 united at base and carpels united throughout, the slightly 2-lobed stigma only giving 

 external evidence of their number. Magnified several diam. After Berg and Schmidt. 



FIG. 251. Pistil of white potato halved transversely, showing two carpels united at 

 center where their edges form a large placenta on whose surface the ovules arise. 

 Magnified several diam. After Kerner. 



or the union may be complete, with the exception of the 

 stigmas, or it may involve even them (fig. 250). Union may 

 take place in such a way that the edge of each carpel meets 

 its fellow and the edges of neighboring carpels in the center 

 of the compound pistil (fig. 251). In this case the ovulary 



* This phrase may be used for convenience in all cases, even of those 

 pistils in which the carpels were at no time separate. 



