322 A TEXTBOOK OF BOTANY [Ch. VI, 10 



By a combination of the methods here described, our 

 cultivated plants have been developed from their wild 

 ancestors. Obviously the process is a kind of evolution, in 

 which man's needs or fancies play the part of the selecting 

 and preserving agency. The methods do not include any 

 way of originating any desired feature; all we can do is to 

 select, preserve, and intensify such features as nature 

 offers. 



In earlier times most, or all, of man's improvements in 

 plants were without plan or forethought, his selection being 

 made upon features which pleased him, or seemed profitable, 

 at the moment; and it is only because in general he has 

 continued to be pleased by the same things that our culti- 

 vated plants have been brought to their present high de- 

 velopment. In modern times, however, much of the im- 

 provement is accomplished by expert workers who proceed 

 with deliberate forethought and a definite aim in mind. 

 This is typical plant breeding, to which we may confidently 

 look for great triumphs in the future. 



10. The Morphology of Flowers 



Although the flower is physiologically a distinct organ of 

 the plant, having its own primary function of effecting fer- 

 tilization, its structure shows obvious morphological relation 

 to leaves and stem. 



The sepals of flowers are commonly green, and so leaf -like 

 in origin and anatomy as to permit no doubt that they, at 

 least, are morphologically identical with leaves. Besides, 

 the most perfect gradations occur from sepals through bracts 

 to the green leaves of the stem (e.g. Calycanthus)^ Petals, 

 also, despite their difference in color, have a perfectly leaf- 

 like development and anatomy, with an occasional complete 

 gradation to sepals (e.g. Cactus flowers) ; so that they too 

 are morphologically leaves. As to the stamens, the fila- 

 ments correspond to leaves in all the morphological test 

 points, including a transition to petals (e.g. in Water-lilies), 



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