THE INTERDEPENDENCE OF LIVINt; Tll|\(;s 



<)l 



Wriilhl I'Urcc 



Tiger Swallow-tail (Papilio turnns) on rose. 



The Relations between Insects and Flowers 



One of the most interesting symbiotic relationships is that which 



exists between msects and flowers. Flowering plants produce .seed.s 



and fruits, and from 



these come new gen- 

 erations of plants, 



but if it were not for 



the visits of insects, 



many plants would 



not produce seeds. 



Insects visit flowers 



in order to obtain 



nectar, a sugary sub- 

 stance formed by the 



nectar glands, and 



pollen. The glands 



which produce the 



nectar are usually so 



placed that an insect 



has to push its way past the stamens and pistil of the flower in order 



to reach the desired food. In 

 doing this, pollen grains may 

 adhere to the hairy covering of 

 the insect and be transferred to 

 the sticky surface of the upper 

 end of the pistil (stigma). Inside 

 the pollen grains are the male re- 

 productive cells (sperms), while 

 in the ovary of the pistil are 

 held the female reproductive cells 

 (eggs). In order to ha\e develop- 

 ment of a new plant, it is essen- 

 tial for a sperm cell to unite with 

 an egg cell. Pollen grains on the 

 stigma are stimulated to send out 

 hairlike tubes, wiiich j)enetrate 

 the stalk (style) of the j)istil and 

 eventually reach the ovary. The 

 pollen tube carries one or more 



•derminatino: 



anther* 



•filameriti 



ovulell'' 



. .-finicropyle-' 



A longitudinal section of the repro- 

 ductive organs of a flower showing the 

 penetration of a pollen tube through 

 the opening in the pistil called the 

 micropyle, and the growth of the pollen 

 tube to the ovule. 



