420 RELATION TO ENVIRONMENT. 



805. Purpose of the flower. While the ultimate purpose of all 

 plants is the production of seed or its equivalent through which 

 the plant gains distribution and perpetuation, the flower is the 

 specialized part of the seed plant which utilizes the food and 

 energies contributed by other members of the plant organization 

 for the production of seed. In addition to this there are definite 

 functions performed by the members of the flower, which come 

 under the general head of plant work, or flower work. 



806. The calyx, or the sepals. These are chiefly protective, 

 affording protection to the young stamens and carpels in the 

 flower bud. Where the corolla is absent, sepals are usually 

 present and then assume the function of the petals. In a few 

 instances the calyx may possibly ultimately join in the formation 

 of the fruit (examples: the butternut, walnut, hickory). 



807. The corolla, or petals. The petals are partly protective 

 in the bud, but their chief function where well developed seems 

 to be that of attracting insects, which through their visits to the 

 flower aid in "pollination" especially "cross pollination." 



808. The stamens. The stamens ( = microsporophylls) are 

 flower organs for the production of pollen, or pollen-spores 

 ( = microspores). The stalk (not always present) is the filament, 

 the anther is borne on the filament when the latter is present 

 The anther consists of the anther sacs or pollen sacs (microspo- 

 rangium) containing the pollen-spores, and the connective, the 

 sterile tissue lying between and supporting the anther sac. The 

 stamens are usually separate, but sometimes they are united by 

 their filaments, or by their anthers. When the pollen is ripe 

 they open by slits or pores and the pollen is scattered; or in 

 rarer cases the pollen mass (pottinium) is removed through the 

 agency of insects (see Insect pollination, Chap. XLIII). 



809. The pistil. The pistil consists of the "ovary," the style 

 (not always present), and the stigma. These are well shown in 

 a simple pistil, common examples of which are found in the 

 buttercup, marsh marigold, the pea, bean, etc. The simple 

 pistil is equivalent to a carpel ( = macrosporophyll), while the 

 compound pistil consists of two or several carpels joined, as in 



