36 



ELEMENTS OF BOTANY. 



mens, and one 5-celled ovary ; or a 4-merous flower with two sepals, 

 four petals, sixteen to twenty-four stamens, and a 1-celled ovary. In fact, 

 in exogenous plants the numerical arrangement, though commonly in fives 

 or fours, presents almost innumerable exceptions — some, indeed, in which 

 the exact plan is scarcely discernible ; but, be it remembered, it is never 

 completely in threes. In endogenous plants, however, the arrangement by 

 threes is much more uniform and the exceptions much more rare. 



Fig. 65. — A flower of the common lilac— 

 4-merous. 



Fig. G6. — Five-merous flower of a geranium. 



We have seen that the calyx and corolla may be regular or irregular, 

 and that both stamens and pistils are subject to variations also. Another 

 form of irregularity requires attention. 



In many plants there is an imperfection in the flowers, some of them 

 being without stamens, others without pistils. These imperfect flowers 

 may be upon the same plant, or upon different individuals of the same 

 species (Figs. 46 and 47). The common ailanthus, so largely used as a 



Fig. 67.— Pistil of the vine with hypogynous 

 stamens. The corolla and calyx (also hypogy- 

 nous) removed. Enlarged. 



Fig. 68. — Superior ovary of the poppy. 



shade-tree, has flowers with stamens only (staminate) on one individual, 

 and those with pistils only (pistillate) on another. Such plants are termed 

 dioecious; while those with both kinds upon the same individual are 

 termed monoecious. Still others have not only perfect flowers — that is, 

 those with both stamens and pistils — but these imperfect staminate and 

 pistillate flowers also ; such plants are termed polygamous. 



