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chapter one £ Background 



Experimental work is the main concern of this study, but some 

 purely descriptive information on flowering should be helpful. This 

 chapter considers, first, the structure and origin of flowers as dealt 

 with by morphologists. The natural history of certain flowering 

 habits will then be briefly described, and an outline of some of the 

 methods used to "measure" or evaluate flowering concludes the 

 chapter. 



MORPHOLOGY OF FLOWERING 



The word "flower" is commonly used for structures of the 

 greatest variety, from those of the elm, simple and inconspicuous, 

 to the showy, complex blossoms of orchids or sunflowers. Morphol- 

 ogists use the term "flower" to mean a determinate sporogenous 

 shoot bearing carpels. Determinate means of strictly limited 

 growth; sporogenous, bearing the reproductive microspores (male) 

 or megaspores (female). The key portion of this definition, how- 

 ever, is the presence of carpels. 



The carpel, characteristic organ of the angiosperms, or "flower- 

 ing" plants, is an organ bearing and enclosing the ovules; the 

 ovules, in turn, contain the megaspores. Under this definition of a 

 flower, the sporogenous axes of gymnosperms— pine cones, for ex- 

 ample—cannot be considered flowers; the absence of true carpels 

 is one of the major characteristics setting off the gymnosperms— 

 conifers, cycads, and the like— from the angiosperms. Strict use of 

 this definition of a flower of course also eliminates those structures, 



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