VEGETATIVE REPRODUCTION. 24 1 



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

 This union is commonly brought about (1) 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 ornus) 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. 



