30 STRUCTURAL BOTANY. [24, 25. 



is monoecious ( 8 ), as in Oak ; in the latter case, dioe- 

 cious ($ ? ), as in Willow. The term diclinous, denot- 



21 ^WL 



^i\ 



19, Pistillate flower of Balm-of-Gilead. 20, Staminate. 21, Begonia a, staminate ; b, pistillate. 



ing either 8 or $ ? without distinction, is in common 

 use. 



68. A neutral flower is a perianth or calyx only, 

 having neither stamens nor pistils. Such are the ray- 

 flowers of many of the Composite, and of the cymes 

 of Hydrangea, High-cranberry, etc., which in cultiva- 

 tion may all become neutral, as in the Snow-ball. 



69. Unsymmetrical flowers. The term symmetry, 

 as used in Botany, refers to number only. A flower 

 becomes unsymmetrical by the partial development of 

 any set or circle in respect to the number of its 

 organs. The Mustard family, called the Crucifers, 

 afford good examples. 



70. The flowers of Mustard, Cress, etc., are understood to be 4-merous ( 0. 

 The sepals are four, petals four, but the stamens are six and the styles but 

 two. The stamens are arranged in two circles, having two of those in the 

 outer circle suppressed or reduced to mere glands. Two of the carpels are 

 also suppressed (429). In the Mint family and the Figworts one or three of 

 the stamens are generally abortive. Here, while the flowers are ^, the sta- 

 mens are four in some species and only two in others. The missing stamens, 

 however, often appear in the guise of slender processes the rudiments of 

 stamens proving in an interesting manner the natural tendency to sym- 

 metry. 



71. In the ^flowers of Poppy, the sepals are but two; in fy Spring-beauty 

 they are but two; in both cases too few for symmetry. In Larkspur (26) the 

 ^ flowers have but four petals ; and in Monk's-hood (29), also fa the petals 



