XVIIL] BOTANY. 73 



of one carpel (pea, Fig. 27) the placenta will be on 

 the walls of the cavity of the ovary (parietal); so also 

 if two or more carpels are united by their edges only 

 (Fig. 53), the ovules will still be parietal; but if two 

 or more carpels are closed by the infolding of the 

 edges of the carpel! ary leaves as far as the axis of the 

 pistil, and are combined by their sides into one, 

 the ovules will be on the axis of the pistil or on 

 placentas projecting from it (Figs. 36, 37, 52). 



FIG. 52. Axile ovules. FIG. 53. Parietal ovules. 



in. The style consists of a column of cellular 

 tissue continuous with the midrib and margins of the 

 carpellary leaf or leaves, enclosing a core of looser 

 cellular tissue amongst which the pollen tubes (Par. 

 1 08) descend to the ovary. 



112. The stigma occupies the top, or the sides of 

 the top of the style ; or of the ovary if there is no 

 style, and is not covered with epidermis (Par. 6), 

 which would obstruct the descent of the pollen tubes. 

 It is frequently formed either of short loose cells 

 which exude a viscid fluid that holds the pollen grains, 

 and hastens the protrusion of their tubes ; or of long 

 cells, forming tufts of hair, amongst which the pollen- 

 grains become entangled. 



