408 GENERAL MORPHOLOGY OF PLANTS 



labiates (in mints, many legumes, many orchids, etc.), which 

 provides better facilities for insuring cross pollination by insects. 

 The fusion of parts of the flower of different sets follows as in epigy- 

 nous, perigynous or epipelalous flowers. Then parts of the same 

 kind are united by coalescence as msympetalous (petals united) and 

 synsepaloiis (sepals united) flowers, while syncarpous fruits (car- 

 pels united forming a compound pistil) represent the highest con- 

 dition of the development of the carpels. The massing of flowers 

 is also another evidence of progression. The highest expression 

 of this arrangement is seen in the composite flowers where nu- 

 merous small flowers unite to form " heads." In many of these, 

 the outer circle of flowers is conspicuous by the lateral elongation 

 of the corolla tube, which is bright colored and serves to attract 

 insects to the head where there are many proterandrous flowers 

 insuring cross pollination. It is to be noted also that the com- 

 posites have reached the highest stage of the union of parts, and 

 they are recognized as the highest expression of the development 

 of the flower. 



Fifth. The closed seed case. The formation of a closed 

 capsule or case (ovary) containing the ovule, which is an advance 

 over the open seed carpel in the Gymnosperms. 



555. The parts of the flower are modified leaves. The 

 sepals and petals are leaf-like in form. They are leaves which have 

 become modified in their development to serve certain definite 

 useful purposes for the plant, as protecting envelopes while the 

 essential parts of the flower are forming, and the petals often 

 serve to attract insects which aid in cross pollination. In some 

 flowers the sepals are green in color, or the same form as the 

 leaves and arranged in the same way on the stem, as in the wake 

 robin ( Trillium}. In this same plant the petals sometimes take 

 on a green color, and thus more clearly show that as members of 

 the plant body they are leaves (floral leaves). This transfor- 

 mation of the sepals and petals to leaves also occurs now and then 

 in many other plants. The stamens and pistils (carpels rather) 

 are also modified leaves. Their leaf nature is sometimes mani- 

 fest, under peculiar conditions, when the stamens and pistils 



