CHAPTER XXXIl 



FLOWERS, FRUITS, AND SEEDS 



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Flowers are the precursors of fruits and seeds, and within the seeds are 

 the embryos of a new generation of plants. The growth of the parts of a 

 flower from the primordia in a flower bud is but the first of a series of 

 processes and structures that ultimately result in sexual reproduction in 

 seed plants. As we proceed with further chapters some of the interrela- 

 tions of sexual reproduction and other plant phenomena will become 

 evident. 



The rapid expansion of an opening flower is mainly the result of cell 

 enlargement by growth of cell walls accompanied by the osmotic absorp- 

 tion of water. Most of the cell division and a considerable amount of 

 cell differentiation, including the differentiation of some of the reproduc- 

 tive cells, occurred in the flower bud before it opened. 



Interest in flowers, however, is not limited to sexual reproduction. The 

 widest general interest lies in the pleasure of seeing them on cultivated 

 plants and also on plants growing under natural conditions. The flowers 

 sold for decorative purposes are valued annually in millions of dollars. 



Flowers are also sources of nectar and perfumes. But the direct eco- 

 nomic importance of flowers is small when compared with the value of 

 the fruits and seeds that develop from them. The accumulated food in 

 these organs is one of the most important commercial products of cul- 

 tivated plants. 



The colors, shapes, and sizes of flowers; the forms and arrangement 

 of the parts of a flower; and the arrangement of flowers and fruits of a 

 plant are as definite as are the fonns and arrangements of leaves. Be- 

 cause of this inherent constancy of form and stmcture, the specific dif- 

 ferences in flowers and fruits, as well as in leaves and stems, are used in 

 classifying plants. Some appreciation of this use of flowers may be gained 

 first-hand by comparing the flowers of a few common plants such as lily, 

 bean, tomato, mint, morning glory, rose, carrot, and sunflower. 



The flower. Numerous flowers are commonly recognized by their 

 form, color, texture, fragrance, or other distinguishing feature. In fact, 



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