SYMMETRICAL FLOWERS 



2,1 



the characteristic form and function of all the parts of one kind. For 

 the identification of the parts of a typical flower, the few illustrations and 

 definitions already given will prove ample, but such flowers are very 

 rare. The great majority of them deviate from the type in one or more 

 directions to such a degree and in such a variety as to very frequently 

 create difficulty in identifying or circumscribing the several parts. To 

 fit the student for properly meeting the difficulties which so arise, as 

 well as for understanding botanical terminology, it is necessary to 

 specify and explain the principal forms of variation and to establish such 

 a classification of them as their varied nature will permit. 



Law 1: Symmetrical Flowers. — The number of parts of each kind or 

 series is the same as of each other, or they have a common multiple. The 

 term Isomerous is used to indicate that the same number of parts enter 

 into the formation of the two or more circles to which the term is applied. 

 In the case of the gynaecium, it is the carpels which are counted as 

 parts of the circle or series, whether developed each as a separate pistil, 

 or all united into one. The number of stamens is normally equal to 

 that of the sepals and petals combined, that is, they form two circles. 

 If the flower is typical, the number of stamens will thus be just twice as 

 great as that of the parts of any other kind. A flower constructed in 

 accordance with this law is called Symmetrical. 



Fig. 25. Apparently monomerous flower of Hippuris. a, calyx; c, stamen: d, pistil. 26. Longitu- 

 dinal section of same. 27. Dimerous flower of Bicuculla. a, sepals; &, original petals; b', petal-like 

 bodies developed from one pair of stamens; c, the other pair of stamens, each divided into three; d, 

 pistil; e, cross-section of ovary, showing two placentae. 28. Trimerous flower of VeratruTn. 29. 

 Tetramerous flower of Oenothera. 30. Pentamerous flower of Geranium, 



Terms Indicating Numerical Symmetry. — Thus, the flower of Hipjpuris 

 (Figs. 25 and 26) has an entire calyx, apparently of one sepal, no corolla, 



