CROSS SECTION OF A CACTUS 

 BLOSSOM 



This is what is called a perfect 

 flower that is to say, one that has both 

 stamens and pistil. The stam.ens are 

 grouped in a circle about the pistil as 

 in the case of the poppy; this being the 

 typical arrangement. The picture 

 shows the seed case or ovary at the 

 base of the pistil. Each ovule must re- 

 ceive the nucleus of a pollen grain or it 

 will not develop. Where the stamens 

 are thus clustered about the pistil, cross- 

 fertilization is usually prevented by 

 the maturing of the two sets of organs 

 at different periods. 



