192 THE REPRODUCTIVE ORGANS 



a union of sepals and petals, production of honey and scent, 

 and at the end of the series we arrive at special forms with 

 irregular flowers. These are so constructed as to exclude 

 the lower forms of insects, but are attractive to and visited 

 by the higher and more intelligent forms, e. g. bees, moths, 

 and butterflies. 



Colour-changes follow somewhat similar lines of develop- 

 ment. The simpler flowers are small, green, and incon- 

 spicuous, a stage higher the petals are larger and yellow or 

 white, while the tubular and more complex flowers are 

 often red, blue, or violet. 



(2) The Morphological point of view, which regards the 

 structural differences, forms, and relationships, of the parts of 

 the flower. If we summarize the chief structural differences 

 we find that the small and simple flowers of the Poplar and 

 Willow have no calyx or corolla. Their flowers are uni- 

 sexual and arranged in catkins, the male and female catkins 

 occurring on different trees, i. e. they are dioecious. In the 

 Oak and Hazel both male and female catkins occur on the 

 same tree, i. e. they are monoecious. The Anemone, Butter- 

 cup, Marsh Marigold, Columbine, Monkshood, and Larkspur 

 are hermaphrodite, and though differing much in form and 

 colour, all agree in possessing a free calyx and corolla, 

 numerous hypogynous stamens, and a superior apocarpous 

 pistil. The perianth is whorled or cyclic, but the stamens 

 and carpels are arranged spirally on the axis. The Stock 

 agrees with the above in that the sepals and petals are free, 

 but there are only six stamens, four long and two short. 

 The ovary consists of two united carpels, divided by 

 a central plate. All the whorls are cyclic. The Violet, 

 while having free sepals and petals, has an irregular corolla, 

 one petal being spurred. The pistil consists of three united 

 carpels and a one-celled ovary. 



Important differences from the above are met with in 



