THE STAMENS. 279 



514. The petals are sometimes furnished with appendages on 

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

 Silene (Fig. 378, 449), and the scales similarly situated on the 

 gamopetalous corolla of the Comfrey, &c. These appendages some- 

 times represent a circle of sterile and metamorphosed stamens ; but 

 more commonly they seem really to belong to the petal. 



515. As to duration, sometimes the floral envelopes are caducous, 

 I. e. falling off when the blossom opens, as the calyx in the Poppy fam- 

 ily and the corolla of the Grape- Vine (Fig. 384). More commonly 

 they are deciduous, or fall after expansion, but before the fruit forms. 

 When they remain until the fruit is formed or matured, they are 

 persistent, which is often the case with the calyx, especially when 

 it has a green color and foliaceous texture. When they persist in a 

 dry or withering state, as the corolla of Heaths, Ciunpanula, &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, 

 345). 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 matter, — a pro- 

 cess which appears to be needful in flowering, and to subserve some 

 important end at the time (368-373). 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 generally reduced to slender bundles 

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



Sect. VI. The Stamens. 



517. The Stamens have already been considered in a general way 

 (418). Before describing their structure more particularly, the 

 principal terms which relate to their number, connection, and posi- 

 tion may be mentioned. Most of these terms were devised by Lin- 

 naeus as names of the classes of his Artificial System of classification 

 (Part n. Chap. IV.), founded mainly upon characters furnished by 

 the stamens. Their number in a flower is accordingly expressed 

 by the names of the eleven or twelve earlier Linnrean classes (990), 

 put into adjective form. Thus, a flower with one stamen is said to 

 be monandrous ; with two, diaridrous ; with three, triandrous ; with 

 four, tetrandrous ; with five, pentandrous ; with six, hexandrous ; 



