120 



COMPOUND ORGANS OF PLANTS. 



together on its flat or convex surface. What are called com- 

 pound flowers, as the Helianthemum, Aster and Dandelion, are 

 heads of this nature, surrounded by a common involucre of bracts. 

 This flat, dilated receptacle, is very conspicuous in the Dande- 

 lion after its ripe pericarps have been removed by the wind. 



If the spike be succulent and covered with unisexual flowers, 

 ordinarily incomplete, that is to say, without floral envelopes, 

 and if the whole be enclosed in a spathe, the inflorescence is 

 called a spadix, as in Arum maculatum, (Fig. 24.) 



If the spike be covered with unisexual flowers, male or 

 female, borne in the axils of bracts, the axis of the spike being 

 articulated at its base so that it is detached and falls off all in 

 one piece, the inflorescence is termed an amentum or catkin, 

 (Fig. 25.) 



Fig. 24. Fig. 25. 



Fig. 25. a Unisexual amGntum of the hornbeam (Carpinus hetuliis.) b. One of the 

 flowers with its subteoding bract magnified. 



