THE ABBAN6EMENT OF THE FLOWERS 



191 



the umbel is compound; that is, secondary umbels, or umbellets, 

 are borne on the ends of the rays (as the pedicels of an umbel are 

 often called). The bracts which subtend the pedicels in the raceme 

 and corymb become verticillate under the umbel, or form an in- 

 volucre; and the umbellets may be pro- 

 vided with involucels. A last year's umbel 

 of the carrot (Fig. 187) is seen to bear the 

 remains of umbellets. 



220. The inflorescence of the 

 common arrow- leaf is seen in Fig. 

 188. It is somewhat corymbose, 

 for the lowest flowers open first. 

 The axis elongates after flower- 

 ing begins, so that the individ- 

 ual clusters are widely separated. 

 The inflorescence appeals to one, 

 therefore, as a series of whorled 

 clusters. In other words, when 

 the parts of an inflorescence 

 are widely separated, particularly 

 by subsequent growth of the axis, 

 the inflorescence is described in 

 terms of its parts, and not as a 

 whole. Such a method of flow- 

 ermg may be called a progressive 

 inflorescence. 



Fig. 188. 



Three-flowered whorls of 

 arrow-leaf. 

 220a. The arrow-leaf or sagittaria is inter- 

 esting because the flowers (as also the parts of the perianth) are 

 in threes, the significance of which may be suggested later. The 

 lower flowers are commonly pistillate and the upper ones staminate. 



