Flowers. 201 



to secure cross pollination, simply prohibits self pollina- 

 tion by its tubular stigmas and its relatively short and 

 reflexed stamens; and then, the sticky pollen and an 

 abundance of ovules being provided, the performance of 

 pollination is intrusted to the wise instinct of the Pronuba 

 moth ; and not pollination simply, but cross pollination, for 

 it has been noticed that it is the habit of the moth after 

 securing the pollen to fly to another flower before it begins 

 to lay its eggs. We wonder how such an instinct could have 

 been evolved, and how the moth and the plant came to be 

 so intimately associated and so absolutely necessary to each 

 other's existence. It seems certain that they have come 

 through the long years of their race history together, and 

 that each has been affected by the modifications of the other. 



Sufficient illustrations have now been given to show the 

 student that there is a wide and attractive field for study 

 in the structure and behavior of flowers ; for they afford 

 us not only the best evidence of the relationships of plants 

 (see Chapter XVII), but they also reveal to us a mutually 

 beneficent association of plants and animals, and the mar- 

 velous plasticity of plants in molding the foirms of their 

 parts and responding to external forces and internal condi- 

 tions in such a way as to meet any required end. 



142. The Morphology of a Flower. — In doing the work 

 in the chapter on Modified Parts, the student has become 

 familiar with the methods of seeking out morphological 

 evidence, and he should now test, with all the evidence 

 obtainable by him, the following statement of the morphol- 

 ogy of a flower: A flower is a branch with much shortened 

 internodes (termed the receptacle) whose growth in length 

 is terminated by the production of spore-bearing leaves 

 (stamens and carpels) ; the most complete flowers also 

 having modified leaves in the form of sepals and petals. 



