190 



BEACTS OK FLORAL LEAVES. 



Bracts are occasionally persistent, remaining long attached to the 

 base of the peduncles, but more usually they are deciduous, falling 

 off early by an articulation. In some instances they form part of the 

 fruit, becoming incorporated with other organs. Thus, the cones of 

 Mrs (figs. 217, 218) and the strobili of the 

 Hop are composed of a series of bracts 

 arranged in a spiral manner, and covering 

 fertile flowers ; and the scales on the fruit 

 of the Pine-apple (fig. 280 a) are of the 

 same nature. In Amenta or catkins (fig. 

 259) the bracts are called squamce or scales. 

 As regards their arrangement, they follow 

 the same law as leaves ; being alternate, 

 opposite, or verticillate. 



At the base of the general umbel in 

 umbelliferous plants, a whorl of bracts often 

 exists, called a general involucre (&g. 262 i'), 

 and at the base of the smaller umbels or 

 umbellules there is a similar leafy whorl 

 called involucel or partial involucre (fig. 

 262 i"). In Compositse, the name involucre 

 is applied to the leaves, scales, or phyllaries, 

 surrounding the head of flowers (fig. 263 

 6), as in Dandelion, Daisy, Artichoke. This involucre is frequently 

 composed of several rows of leaflets, which are either of the same or 

 of different forms and lengths, and often lie over each other in an im- 

 bricated manner. When the bracts are arranged in two rows, and 

 the outer row is perceptibly smaller than the inner, the involucre is 

 sometimes said to be caliculate, as in Senecio. The leaves of the in- 

 volucre are spiny in Thistles and in Dipsacus (fig. 265, e i), and hooked 

 in Burdock. Such whorled or verticillate bracts may either remain 

 separate (polyphyllous), or may be united by cohesion (gamophyllous), as 

 in many species of Bupleurum, and in Lavatera. In the acorn they 

 form the cupula or cup (fig. 281, c), and they also form the husky 

 covering of the Hazel-nut. In the yew the bracts form a succulent 

 covering of the seed. 



When bracts become united together, and overlie each other in 

 several rows, it often happens that the outer ones do not produce 

 flowers, that is, are empty or sterile. In the artichoke, the outer 

 imbricated scales or bracts are in this condition, and it is from the 

 membranous white scales or bracts (yaleai) forming the choke attached 



Fig. 280. Fmit of Pine-apple {Ancmassa satvva), composed of numerous flowers united 

 into one mass ; the scales, a, being modified bracts qr floral leaves. The crown, b, consists 

 of a prolongation of the axis bearing leaves, which may be considered as a series of empty 

 bracts, ie. bracts not producing flowers in their axiL 



Fig. 280. 



