226 FLOWER-LAND. 



Perispenn. See Endosperm. 



Parasites, Saprophytes. Some flowering plants have no 

 chlorophyll, and so they cannot take in carbon by assimilation. 

 They are consequently obliged to take their carbon, which is 

 necessary to their life, combined with something else, that is, as 

 I have called it, prepared food (p. 200). When they do this from 

 other living plants, they are called parasites. If they take it from 

 the decayed remains of plants they are called saprophytes. The 

 mistletoe has green leaves and is only partly parasitic (p. 75). 



Placentation means the way in which the ovules are attached or 

 placed within the ovary. This varies with the different kinds of 

 ovaries, and you will understand the different kinds of placentation 

 more easily if you remember that the ovules are usually upon the 

 margins of the carpel leaves. 



(i.) So if the ovary be simply monomerous and unilocular, since 

 the ovules are upon the margins of the carpel leaf, they are just 

 inside and along each side of the ventral suture (p. 116). Their 

 placentation or attachment is therefore described as marginal or 

 sutural placentation (Fig. 102 A, p. 119). 



(ii.) But now suppose the ovary is polymerous and unilocular. 

 Here the margins of the carpel leaves simply join, as in Fig. 102 

 B, / being their junction, that is the placenta. Or the carpel 

 leaves may be turned in so as to form a unilocular but chambered 

 ovary (p. 119), as in Fig. 102 C, p showing the placenta. In this 

 case, as the ovules are upon the walls or partial dissepiments of the 

 ovary, their placentation is called parietal * placentation. 



(iii.) But if the ovary is polymerous and multilocular, then the 

 dissepiments reach the centre of the ovary, as in Fig. 102 D, and 

 the placentas / are upon a central column or axis. In this case, 

 because the ovules are thus upon the axis, the placentation is 

 called axile. 



(iv.) If in a polynlerous multilocular ovary the dissepiments fall 

 away, the ovules are left upon the axis in a unilocular or chambered 

 ovary. Their placentation is then called free central placentation. 



* From the Latin "paries" a wall. 



