32 



ELEMENTS OF BOTANY. 



numerous, and each separate and distinct, or all may be wholly or partly 

 united. 



When the petals are distinct the corolla is termed polypetalous 

 (Fig. 55); when they are united it is termed mono- or gamopetalous 

 (Fig. 56). In the gamopetalous corolla there is the same distinction of 

 tube, throat, limb, and lobes as in the gamosejoalous calyx, and it is de- 

 veloped in the same manner — by the fusion of originally distinct leaflets. 

 It may likewise be regular (Figs. 55 and 56) or irregular (Figs. 57 and 58), 

 and though commonly deciduous, it is sometimes withering-persistent 

 — that is, withering but not falling away from the maturing fruit. In 

 short, the corolla is very like the calyx, save that it is much more delicate 

 in structure, more beautiful in form, and often most exquisitely colored. 



Fig. 55. — Polypetalous corolla of a wild rose. 



Fig. 56.— Monopetalous 

 corolla ami monosepalous 

 calyx of tobacco. 



Fig. 57.— Irrogular co- 

 rolla of aconite. 



It is not unfrequently absent ; then the flower is called apetalous. In 

 this case the calyx is often colored like a corolla, and therefore well sup- 

 phes its place. But in many plants both calyx and corolla are wanting ; 

 then the flowers are termed naked. 



The essential floral organs, as remarked above, are the stamens and pis- 

 tils. The stamens are variable in number, and commonly form a circle 

 within the coroUa if this be present, or in its absence within the calj'x. 

 They are the fertilizing organs, or, according to the former ideas of the 

 sexuality of plants, they supply the male element in the process of repro- 

 duction. 



A stamen consists of two parts, an anther and a stalk or filament 

 upon which this is supported (Fig. 59). The anther is the only essential 

 part, and this may be and often is sessile. It consists of two cells, di- 

 vided from each other vertically by a septum, each opening at maturity and 

 yielding a cellular, powdery substance — the pollen, which is the fertilizing 



