116 



STRUCTURAL BOTANY. 



suppressed, as in the Cruciferre. Often they are colored, some- 

 times brilliantly, as in Painted-cup. Sometimes they are scalo- 

 like, and again they are evanescent membranes. 



346. The Spathe is a large bract formed in some of the Mono- 

 cotyledons, enveloping the inflorescence, and often colored, as in 

 Arum, Calla ; or membranous, as in Onion and Daffodil. 



347. Bracts also constitute an Involucre when they are col- 

 lected into a whorl or spiral group. In the Phlox, Dodecatheon, 

 and generally, the involucre is green, but sometimes colored and 

 petaloid, as in Dogwood and Euphorbia. Situated at the base 

 of a compound umbel, it is called a general involucre ; at the 

 base of a partial umbel it is a partial involucre or involucel, 

 both of which are seen in the Umbelliferre. 



433, Heliuuthns grosse-serratus I, involucre; r, rays, or ligulate flowers. 434, One of the disk-flowers 

 with its chaff-scale (bract). 435. Acorn of Moss-cup Oak (Q. macrophylla). 436. Poa pratensis/; spike- 

 let entire ; g, glumes separated ; c, a flower separated, displaying the two pales, 3 stamens and 2 styles. 



348. In the Compositre, where the flowers are crowded upon a 

 common torus, forming what is called a compound flower, an in- 

 volucre composed of many imbricated scales (bracts) surrounds 

 them as a calyx surrounds a simple flower. The chaff also upon 

 the torus are bracts to which each floret is axillary (434). 



349. In the Grasses, the bracts subsist under the general name 

 of chaff. At the base of each spikelet (436) of flowers we find 

 two bracts the Glumes. At the base of each separate flower 

 in the spikelet are also two bractlets the Pales en ve- oping as 

 a calyx the three stamens and two styles (c). 



350. The cup of the Acorn is another example of involucre, 



