THE PATH OF EVOLUTION 



isms may better supply the elements or conditions 

 needed for the fertilized ovule that otherwise might 

 be deficient if one plant only furnished all. The 

 varying conditions of soil and exposure to light and 

 moisture must also cause variations in structure in 

 each plant, and give rise to such slight differences in 

 constitution as to be favorable to greater perfection in 

 the pollen and induce such changes as to lead to the 

 higher evolution of its structure and functions. Be 

 the cause what it may, and the principles of evolution 

 best account for it, the fact is certain that the most 

 intricate devices exist in innumerable instances by 

 which the pollen immediately adjacent is excluded, 

 and fertilization made possible only by the pollen 

 being brought from other flowers by the wind, or 

 very frequently by insects or birds, who seek the 

 flowers that are far apart for the honey or other 

 food secreted respectively for their attraction. 



All flowers consist essentially of three distinct 

 parts, all of which arise from modifications of the 

 ordinary leaf of the plant. They are, first, the 

 outer protecting envelopes, consisting of the calyx or 

 lower cup-like leaves or sepals (often greenish and ad- 

 joining the stem), and the corolla or petals. The latter 

 are usually the most conspicuous part of the flower, 

 being often brilliantly colored and their texture 

 exquisitely soft and delicate. The sepals and petals 



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