548 



BOTANY 



PART II 



The placentation is termed PARIETAL when the placentas form projections 

 from the inner surface of the wall of the ovary (Fig. 516 D}. If the margins of 

 the carpels project farther into the ovary, and divide its cavity into chambers or 

 loculi, the placentas are correspondingly altered in position, and the placentation 

 becomes AXILE (Fig. 516 B}. In contrast to such TRUE SEPTA, formed of the 

 marginal portions of the carpels, those that arise as outgrowths of the surface or 



FIG. 516. Transverse sections of ovaries. A, Lobelia B, Diapensia ; C, Rhododendron ; 

 D, Passiflora ; pi, placenta ; sa, ovules. (After LE MAOUT and DECAISNE.) 



sutures of the carpels, as in the Cruciferae, are called FALSE SEPTA (Fig. 656). By 

 the upgrowth of the floral axis in the centre of the ovary what is known as FREE 

 CENTRAL PLACENTATION comes about (e.g. Primulaceae). The projecting axis 

 cannot be sharply distinguished from the tissue of the carpels. The septa, which 

 were originally present, are arrested at an early stage of development or com- 

 pletely disappear, so that the ovules are borne on the central axis covered with 

 carpellary tissue and enclosed in a wall formed by the outer portions of the carpels. 



A 



FIG. 517. Different forms of gynaecea. A, Of AconUum Napcllus ; B, of Linum usitatissimum ; 

 C, of Nicotiana rustica ; D, style and stigma of Achillea miUefolium ; /, ovary ; g, style ; 

 n, stigma. (After BERG and SCHMIDT, magnified.) 



Each carpel in an apocarpous gynaeceum is usually prolonged above 

 into a stalk-like STYLE terminating in a variously-shaped STIGMA. The 

 stigma serves as the receptive apparatus for the pollen, and in relation 

 to this is often papillate or moist and sticky (Fig. 517 D). When 



