INDETERMINATE INFLORESCENCE. 



215 



times (as in Cornus Florida, or tlie common Dogwood, and C. Cana- 

 densis, Fig. 321) becoming petal-like, and much more showy than 

 the blossom itself. Here it is at once distinguished from the calyx 

 or corolla by its including a number of flowers. Sometimes, how- 

 ever, as in the Mallow and Hibiscus, the involucre forms a kind 

 of outer calyx to each flower. 



394. The axis, or rhachis (382), of a head is called its Recep- 

 tacle. Frequently, instead of being globular or oblong, it is flat or 

 depressed, and dilated horizontally, so as to allow a large number of 

 flowers to stand on its level or merely convex surface ; as in the Sun- 

 flower, Aster, Marigold, Dandelion, and Cichory (Fig. 323). Here, 

 as in Fig. 321, a set of bracts form an involucre, surrounding the 

 dense head of flowers. And as the involucre considerably resembles 

 a calyx, while the outer flowers, often of a peculiar sort, are readily 

 mistaken for petals, the head in these and similar plants was called 

 a compound jiower by the 

 older botanists. Fig. 324 rep- 

 resents a section through a 

 head of such flowers in a Co- 

 reopsis ; and Fig. 325 is a slice 

 of the same, more enlarged, 

 displaying some of the sepa- 

 rate flowers. In Coreopsis, 



as in the Sunflower, Yarrow, 321 



&c, each blossom of the head is subtended by its bract (b) ; and 

 the bracts in such cases are called Paha or Chaff. 



395. The Fig presents a ease of very singular inflorescence 



FIG 324 Vertical section of a head of flowers of a Coreopsis. 



FIG 325. A slice of Fig 321, more enlarged, with one tubular perfect flower (a) left stand- 

 ing on the receptacle, and subtended by its bract or chaff (b) ; also one ligulate and neutral ray- 

 flower (c), and part of another: <7, section of bracts or leaves of the involucre. 



