144 



INTRODUCTION TO BOTANY 



FIG. 127. Structure of an ear of corn (pistil- 

 late flower cluster) 



A, section of young ear before fertilization of the 

 ovules (grains) ; ax, axis of spike (cob) ; si, ends 

 of silk (styles and stigmas) ; B, magnified sec- 

 tion through a grain, showing bracts around the 

 ovary, the ovule (o), and the base of the style; 

 C, upper portion of style, with the stigmas (st) 

 considerably magnified. After F. L. Sargent 



137. The potato and 

 the grape ; flowers open 

 to all insect visitors. 

 The potato is a famil- 

 iar example of a flower 

 with wide-open corolla 

 (fig. 128), easily entered 

 by any kind of insect. 

 The flowers, with their 

 white corollas and con- 

 ical group of yellow 

 anthers, are moderately 

 conspicuous and are vis- 

 ited by insects for the 

 sake of the pollen which 

 they afford. They yield 

 no nectar. 



The flowers of the 

 grape are small and 

 greenish. The corolla 

 does not expand but 

 falls off in one piece as 

 soon as the flower is 

 mature. This leaves the 

 stamens and pistil ex- 

 posed to all kinds of 

 insect visitors. Insects 

 of various kinds are at- 

 tracted by the sweet 

 odor of the flowers, and 

 find plenty of nectar 

 on the nectar glands 

 which stand almost un- 

 der the ovary between 

 the bases of the fila- 

 ments (fig. 120). 



