206 THE REPRODUCTIVE ORGANS 



and some, often scarlet exotic flowers, are pollinated by 

 humming-birds. 



Positions of honey-glands. Nectaries occur, as we have 

 seen, on many different organs, but usually they are on 

 some part of the flower : 



(a) On the receptacle at the bases of the short stamens 

 in the Wallflower and Stock ; 



(b) On the sepals of the Mallow and Coronilla ; 



(c) On the petals of the Buttercup and Lesser Celandine, 

 and in the spurred petal of Orchis ; 



(d) On the stamens of the Violet and Pansy, the spur 

 acting as a honey-receptacle ; 



(e) On the carpels of the Marsh Marigold and Bluebell. 



Nectaries sometimes occur on leaves (extra-floral nec- 

 taries) (Fig. 219, p. 340). These attract numerous ants, 

 which in turn keep off the caterpillars that would eat the 

 leaves. 



Fertilization and the Origin of Seeds 



Structure of the pistil. The pistil is the inner essential 

 organ of the flower. In a typical and simple case like that 

 of the Pea it may be regarded as an up-rolled leaf (Fig. 139), 

 bearing on its margins small rounded bodies called ovules (0). 

 If we suppose the turned-in edges to meet and fuse, so 

 enclosing the ovules in a box, we can form some idea of its 

 structure. The ovule-bearing portion is called the ovary (ov) , 

 and that part of the edge from which the ovules spring is 

 called the placenta (pi). Its tip is prolonged and known 

 as the style, and at the end of it is a portion which receives 

 the pollen, called the stigma. Such an ovule-bearing leaf 

 is called a carpel, and in the case of the Pea the pistil con- 

 sists of one carpel only. 



In the Stock the pistil is composed of two united carpels ; 

 in the Clematis, Buttercup, Marsh Marigold, and Rose, it 



