THE STAMENS. 289 



their inner surface, such as the crown at the summit of the claw in 

 Silene (Fig. 302), and the scales similarly situated on the gamo- 

 petalous corolla of Myosotis and Symphytum (Ord. Boraginaceee). 

 The nature of this crown has already been explained (458). Such 

 appendages are sometimes thought to represent an adherent row 

 of abortive stamens or petals. 



514. The bodies termed nectaries (485) by the old botanists are 

 either petals of unusual form, such as the spurs of the Columbine ; 

 or petals passing into stamens, such as the fringe of the Passion- 

 flower ; or a deduplication of the petal, as in Parnassia (Fig. 305) ; 

 or else abortive and transformed stamens, as in Canna. The 

 so-called nectary of Orchidaceous plants is merely a petal, which, 

 being of a different shape from the others, is termed the labeUum. 



515. The duration of the floral envelopes varies greatly in dif- 

 ferent plants. Sometimes they fall off as the flower opens, or even 

 before expansion, as the calyx of the Poppy and the corolla of the 

 Grape-vine (Fig. 334) ; when they are said to be caducous. More 

 commonly they are deciduous, or fall after anthesis but before the 

 fruit forms. When they remain until the fruit is formed or ma- 

 tured, they are persistent, which is often the case with the calyx, 

 especially when it has a green color and foliaceous texture. It is 

 occasionally accrescent, or takes a farther growth during fructifica- 

 tion, as in Physalis. When the envelopes persist in a dry or with- 

 ering state, as the corolla of Heaths, of Campanula, &c., they are 

 said to be marcescent. 



516. Besides serving as organs of protection, the sepals, when 

 green, assimilate sap, and act upon the air like ordinary foliage 

 (344, 346). The petals, like other uncolored (that is greenless) 

 parts, do not evolve oxygen, but abstract it from the air, and give 

 off carbonic acid ; in other words, they decompose assimilated mat- 

 ter, a process which appears to be needful in flowering, and to 

 subserve some important end at the time (367-373). The tissue 

 of a petal is much the same as that of a leaf, except that it is much 

 more delicate, and the fibro-vascular system is reduced to slender 

 bundles of a few spiral vessels, &c., which form its veins. 



SECT. VI. THE STAMENS. 



517. The Stamens, collectively forming the ANDRCECIUM (418), 

 have been already considered in respect to their component parts, 



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