Flowers and Flower Clusters 



241 



are caught and in which they germinate. The pistils and stamens 



are called the '' essential organs " of the flower, because they 



produce the ovules and pollen 



which are the two elements 



necessary in the production of 



seed. 



Fig. 148. Epidermis from the petal of a 

 geranium. The velvety appearance of many 

 leaves and flowers is due to similar projec- 

 tions of the epidermal cells. 



Pistils are variously con- 

 structed out of one or more 

 leaf-like parts called carpels. 

 For example, the pod of the 

 bean or pea is composed of a 

 single carpel. It may be com- 

 pared to a simple leaf folded at 

 the midrib, with the margin united. The fruit of the yucca, 

 tulip, and lily is composed of three carpels. The apple, pear, 

 and quince pistils are made up of five carpels, which constitute 

 the hard papery walls of the seed cavities in the '' core." 



The variety of floral structures. The above is a description of a 

 typical flower ; but in the plant world we find an almost endless 

 variation in the number, form, size, color, and arrangement of 



"^^^H. 



Figs. 149 and 150. Cross-sections of the "essential organs" of a flower. At the left, an- 

 ther of a lily, showing the four microsporangia and the contained pollen (microspores) ; 

 at the right, ovulary of a lily, showing six of the ovules, arranged in pairs within the three 

 carpels. 



