80 



MORPHOLOGY, OR COMPARATIVE ANATOMY. 



Umbels usually have an involucre at the base of the radii, as noted 

 above. The simple umbels of the Onion group are originally enclosed in 

 a membranous spathe. 



Capitulum or Head, The capitulum is mostly formed by the 

 rachis expanding into a thickened mass, surrounded by an involucre 

 of overlapping bracts, presenting a convex, flat, or concave surface 

 (common receptacle), upon which are crowded a great number of 

 sessile flowers, as in the families of Composite and Dipsaceae 

 (figs. 141-146). In the Composite there are often little mem- 

 Fig. 141. Fig. 142. Fig. 143. Fig. 144. 



A 



Fig. 141. Capitulum of Scabioaa. 



Fig. 142, Vertical section of the capitulum of Scablosa. 

 Fig. 143. Receptacle of the Daisy with the florets removed. 

 Fig. 144. Receptacle of Dandelion with the florets removed ; bracts of the 

 involucre reflexed. 



Fig. 146. 



Fig. 145. 



Fig. 145. Section of a capitulum of a Composite plant with palese at.the base of the central 



tubular and of the marginal ligulate florets. 

 Fig. 146. Section of an empty capitulum of a Composite plant with a paleaceous receptacle. 



branous bracts (palzce) at the outside of each flower (figs. 145, 146) ; 

 in the Dipsaceae each flower is surrounded by a cup-like involucel 

 (fig. 142). 



The flowers crowded together in the capitula of Composite are small 

 and of various forms, so arranged as to give the whole the outward aspect 

 of a single flower ; hence this inflorescence was formerly called a compound 

 Jloicer, and its involucre a common cahjx. 





