GYN^CIUM 65 



placentation. When the ovules are attached to the walls of 

 the ovary the placentation ii, parietal (fig. 93, e.g. Violet, Poppy, 

 Wallflower, Pea) ; an ovary with parietal placentas is usually 

 one - chambered, but in the Wallflower-family the ovary has 

 two parietal placentas, and yet is two-chambered. When the 

 ovary is syncarpous and has several chambers, and the ovules 

 are attached to the central axis of the ovary (where the carpels 

 meet), the placentation is axile (fig. 94, e.g. Hyacinth). If a 

 chamber of an ovary contains only one ovule which is attached 

 to its floor, the placentation is basal (e.g. Buttercup). Finally, 

 when the ovary is one-chambered, and possesses a number 

 of ovules attached to a swelling springing from the floor of 

 the ovary, the placentation is central {e.g. Chickweed) or free- 

 central (fig. 95, e.g. Primrose). 



Methods of ascertaining the number of carpels which compose 

 a syncarpous gyncRcium. — By definition a syncarpous gynaecium 

 consists of several carpels joined together. The following rules 

 enable us to learn how many carpels enter into the composition 

 of an ovary : — 



(i.) When an ovary has several chambers, each chamber 

 represents one carpel.* 



(ii.) If the ovary be one-chambered and the placentation 

 parietal, the placentas correspond with the joined ventral sutures 

 (margins) of the carpels, and consequently denote the number 

 of carpels. 



(iii.) If there be several styles, style-branches, or stigma-lobes, 

 their number corresponds with the number of the carpels. 

 Occasionally, however, the styles or stigmas branch so that 

 this rule does not hold. 



(iv.) When the fruit is ripe, the wall of the ovary frequently 

 opens along as many lines as there are carpels. 



(v. and vi.) Development, and comparison with closely- 

 related plants, often aid us in determining the number of 

 carpels (see next chapter). 



As examples of the application of these methods, we may 

 select the two cases. The Pea has a one-chambered ovary, 

 with one style, one stigma, and one parietal placenta down one 

 side. The gynaecium, therefore, consists of one carpel and 

 is apocarpous, in spite of the fact that in the fruit-condition 



* Exceptions to this rule occur in the Labiatse and Boraginaceae. 



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