DKSCRIPTIVE BOTANY. 



round the peduncle, it is termed an " involucrum ; " 

 and in some cases they cohere by their edges, and 

 thus form a single piece. Where the bractea, or rather 

 involucrum, is very large, and completely envelopes the 

 flowers, as in the Aroideae, it is called a " spathe" 

 (fig. 88. a). In the extensive order 

 Composite, the little florets are crowded on 

 a highly dilated receptacle, as in the com- 

 mon daisy and dandelion ; and they are 

 closely surrounded by an involucrum 

 (fig. 87. ), composed of many bracteae, 

 which are either free, or adhere together, 

 and the whole head has the appearance of 

 a single flower. The cup in which the 

 acorn is placed, is an involucrum, com- 

 posed of several whorls of bracteae, all 

 adhering, and blended together into a solid 

 mass (fig. 118.). 



(92.) Floral Whorls. The foliaceous 

 appendages which succeed the bracteae in 

 the order of development, are brought close together, 

 by the non-extension of the axis, so as to crown the 

 summit of the flower-stalk with a series of whorls, 

 partaking still less of the leafy character than the bractea? 

 (art. 86.). These whorls constitute the flower; and 

 the portion of the axis on which they are seated, is 

 termed the torus, which bears the same relation to 

 a single flower, as the receptacle does to a head of 

 flowers. 



In flowers which possess the greatest number of 

 whorls, such as those of the natural order Ranuncu- 

 laceae, we may distinguish four different kinds of organs; 

 two of which, composing the outermost whorls, are col- 

 lectively termed the " perianth ; " and these are not 

 essential to the fertility of the plant ; but the two 

 kinds which make up the innermost whorls, are abso- 

 lutely requisite to secure the perfection of the seed. It is 

 not necessary, indeed, that both the latter kinds should 



