190 



ORGANOGRAPHY. 



Fir cones {figs. 269 and 397) show in a marked manner a spiral 

 arrangement. 



Bracts vary in their duration ; when they fall immediately, or 

 soon after the flower-bud expands, they are said to be deciduous. 

 When they remain long united to the floral axis, they are persis- 

 tent. In some plants, they remain and form a part of the fruit; 

 thus, in the Nut and Filbert they form the husk (fig. 378), in the 

 Acorn they constitute the cup (fig. 377), and in the Hop- fruit 

 (fig. 398), in the Fir-cones (figs. 269 and 397), and Pine-apple 

 (fig. 706, 2), they persist as membranous, woody, or fleshy 

 Bcaly appendages- 

 Certain varieties of arrangement and forms of bracts have 

 received special names. Thus the bracts of that kind of in- 

 florescence called an Amentum or Catkin (fig. 374), as in the 

 Willow, Oak, Birch, &c., arc termed squama or scales. 



Fig. 375. 



Fig. 374. 



Fiff. 374. Male catkin of the Hazel, showing a number of scaly bracts 



between tlie flowers /•'/>/. 37.5. Comjjouiid umbel of the Carrot C-DaMCits 



Carotu). a. General involucre, b. Partial involucre. 



When a circle or whorl of bracts is placed round one flower, 

 as in the Mallow (fig. 372) and Striiwbcrry (fig. 373), or a 

 number of flowers, as in the Carrot (fig. 375), and many um- 

 hcllifcrous phmts, they form what is termed an involucre. In 

 some umbclhfcrous plants, as for instance the Carrot (fig. 375), 

 there arc two kinds of involucre, one at the base of the primary 

 divisions of tlic floral axis or general umbel («); and another 

 at the base of each of the partial umbels orumbellulcs (b); the 

 former is then called the general involucre; and each of the 

 latter an involuccl or partial involucre. In ])lants of the natural 

 order Composita;, as the Marygold (fig. 376), Artichoke, 



