THE LOWER DICOTYLEDONS. 



327 



Fig. 130. Floral Di 

 gram of a Poppy. 



are numerous and have curved filaments, arching over the 

 pistil. The outer stamens open first, moving outwards as 

 they shed their pollen. See Figs. 129, 130. 



The pistil has a peculiar structure. It consists of a rounded 

 top- shaped ovary, crowned by a radiating series of stigmas 

 (8 to 12), forming ridges on the convex 

 roof of the ovary. This roof projects over 

 the ovary at the edges, and on cutting 

 across the ovary just below the " eaves " of 

 this roof you will see that the cavity of the 

 ovary appears to be partitioned up by a 

 series of radiating plates corresponding in 

 number and in position with the stigmatic 

 ridges. The plates, or placentas, covered 

 with numerous ovules, are ingrowths of the 

 ovary wall, but they do not meet at the 

 centre of the ovary cavity, hence the ovary 

 is one-chambered with parietal placentation (Fig. 131). 



In most of the flowers which have this kind of ovary each 

 stigma stands directly over the midrib of a carpel and there- 

 fore between two placentas; the exceptional arrangement 

 seen in the Poppy is explained by regarding each stigmatic 



ridge as corresponding to 

 the fused halves of two 

 adjacent stigmas. When 

 pollen-grains are placed on 

 a stigmatic ridge, the pollen- 

 tubes grow down in the 

 loose conducting tissue of 

 the placenta and emerge on 

 reaching the ovules. 



The Poppy flower con- 

 tains no honey, and is a 

 good example of a pollen - 

 flower, being visited by all 

 sorts of insects for pollen. 

 In crawling about the stamens and stigmas, the insects may 

 effect either cross- or self-pollination. The pollen-grains are, 

 contrary to the general rule in insect-pollinated flowers, little 

 damaged by rain, to which the erect open flower is freely 

 exposed, and appear to be unwettable by water. 



--OVULES 



PLACENTA 



Fig. 131. Section across Ovary of Poppy, 

 showing Placentas bearing the Ovules. 



