IV.] 



ZINNIA. 



35 



coloured petals, is in reality a head of numerous flowers 

 {flower-head). The flower-head is surrounded by a number 

 of scaly leaves, forming an mvolucre^ called by the older 

 botanists a " common calyx." Within the involucre the 

 summit of the stem rises in a conical form, bearing, closely 

 packed upon its surface, the little flowers, called floi-ets, of 



I 



Fig. iq. Garden Zinnia {Zinnia elegans). 



the flower-head. There is a marked difference in form 

 between the outer and inner florets of the flower-head, due 

 to the one-sided enlargement of the corolla in the former. ^ 

 The outer florets with one-sided corollas, taken together, 

 form the ray of the flower-head \ the smaller florets, with 



^ In a recent variety of the Zinnia the flower-heads show a tendency 

 to become "double," by all the florets acquiring the form of corolla, 

 which in the wild state and common varieties is characteristic of the 

 ray-florets only. 



D 2 



