THE FLORAL OROANS. 



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393. CoNVOL0TE, when each leaf wholly involves all that are within 

 it, as do the petals of Magnolia; and vexillary, when one piece larger 

 than the rest is folded over them, as in the pea (251). 



394. Plicate or folded estivation occurs in tubular or monopetalous 

 flowers, and has many varieties, of which the most remarkable is the 

 supervolute, where the projecting folds all turn obliquely in the same 

 direction, as in morning-glory, thorn-apple (Datura). 



Diagrams of flowers (as seen by cross-sections). 253, Joffersonin dipiylla r o, ovary ; «, .«ti- 

 mens ; a, inner vow of petals, sestivation triquetrous ; B, outer row of petals, ajstivation cuntortert ; 

 e, sepals, estivation quincuntial. 254, Lily. 255, Strawberry. 256, Mustard. The pupil will 

 designate the modes of lestivatioa. 



The Eestivation of the sepals often differs from that of tho petals in the sanne 

 flower. Thus, in the pink the sepals are imbricated and the petals contorted. 



:i95. The positigs' on the parts of the flower, with respect to the main 

 axLs and the bract whence it arises, is often important in description. That part 

 wliich ia adjacent to the axis is the posterior or upper, while that which looks to- 

 ward the bract is the anterior or lower part. 



THE FLORAL ORGANS. 



396. Tbchnicai, definition of the flower. The flower is an as- 

 semblage of leaves more delicately and variously formed, borne at the 

 upper nodes of the axis where the internodes are undeveloped. This 

 portion of the axis is called 



397. The receptacle or torus. It is the axis of the flower situ- 

 ated at the summit of the flower-stalk. Its form above is commonly 

 that of a flattened or somewhat conical disk, the center of which cor- 

 responds with the apex of the axis. 



398. The flower may consist of the following members : 1, the 

 floral envelops ; 2, the essential floral organs. 



399. The floral envelops consist of one or more circles or wKorls 

 of leaves surrounding the essential organs. The outer of these whorls 

 is called the calyx and the other, if there be an)-, the corolla. Tho 

 calyx may, therefore, exist without the corolla, but the corolla can not 

 exist without 



400. The calyx. This is a Greek word signifying a cup. It is ap- 

 plied to the external envelop of the flower, consisting of a whorl of 



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