106 



PEACTICAL BOTANY 



Fig. 93. Apetalous flower of buckwheat (Fagopyrum 

 esculentum) 



^■1, flower; 5, section of flower. Both somewhat magnified. 

 After Marchand 



Frequently the arrangement of the floral organs differs from 



that just described by reason of the absence of one or more 



sets of organs or 

 from the multi- 

 plication of the 

 whorls. In the 

 buckwheat, for 

 example (Fig. 

 93), only one 

 whorl surrounds 

 the stamens and 

 pistil. In such 

 cases it is usual 



to assume that the missing flower leaves are the petals, and 



the flower is said to be apetalous (without petals). Sometimes 



neither sepals nor petals are found (Fig. 94). On the other 



hand, many flowers have 



both calyx and corolla, 



with the number of petals 



equal -to that of the 



sepals, but with indefi- 

 nitely numerous stamens, 



as in buttercups. 



96. Unisexual flowers. 



Among many families 



of plants the flowers do 



not contain both stamens 



and pistils. One kind of 



flower has stamens only, 



and is called a staminate 



flower, while the other 



kind has pistils only, and 



is called & pistillate flower 



(Figs. 94 and 96). Such 



flowers are said to be 



unisexual or diclinous. 



Fig. 94. Dicecious flowers of white willow 

 {Salix alba) 



A, staminate catliin, natural size ; B, pistillate 



catkin, natural size; C, a, staminate flower, 



magnified; D, a pistillate flower, magnified. 



After Cosson and De Saint-Pierra 



