ORDER NECESSARIA. 175 



vated as an annual, being spontaneous, in alluvial si- 

 tuations, near the banks of Red River and of the Ar- 

 kansa. This plant attains the height of 3 or 4 feet, 

 is nearly quite smooth, with sessile, ovate, acute, rarely 

 toothed leaves, the upper ones quite entire ; the 

 branches, few in number, are terminated each by a 

 large flower of a pale pink color ; the calyx is extreme- 

 ly curious, having all its imbricated scales terminated 

 by moveable, chaffy, shining processes, pinnatifidly 

 cleft into bristly ciliae. The pappus is hairy, and of 

 unequal length. The rays of Centaurea, often cleft 

 with more than 5 divisions, appear to be double, infer- 

 tile tubular florets, enlarged in size from the absence 

 of all other organs. A transformation of this kind, 

 though acting on uncombined florets, is familiar in the 

 double, or rather monstrous flowers of the common 

 Feverfew (Crysanthcmum Parthenium), where the 

 enlarged tubular florets of the disk are also deprived 

 of the style and stamens. 



NECESSARIA. 



In this order the rays only are fertile, for the cen- 

 tra 1 or discal florets, though to all appearance perfect, 

 are constantly sterile. These plants then are easily 

 known by producing seed on the marginofthe disk only. 



The common Marygold (Calendula officinalis), in 

 almost every garden, affords one of the few examples 

 of this order which are known to exist. The calyx 

 consists of many equal leaves; the receptacle is 

 naked ; the seeds are without pappus, and curved ; 

 those of the disk are imperfect and membranous. 

 The flower is of an orange yellow, and frequently 

 double or monstrous, having all the florets ligulate. 



In the southern, middle, and western states, the sa- 

 vannas, prairies, and mountain meadows, present us 



