DEVELOPMENT OF PLANTS 



451 



contains many familiar native and cultivated plants which may be 

 recognized by the hollow internodes of the stems, leaves variously 

 lobed and attached by conspicuous sheathing petioles, peculiar 

 odors derived from oils and resins, small flowers that are usually 

 white or yellow and grouped into flat-topped inflorescences (um- 

 bels), which are usually surrounded by bracts, called the involucre 

 (Fig. 324, A, B). These features are well seen in the wild carrot 



Fig. 324. A common form of the Umbellales: A, stems of wild carrot 

 (Daucus) with flowers arranged in compound umbels. B, inflorescence with 

 all the umbels removed but one — in, bracts of the involucre. C, forms of 

 flowers, the one on the right being a flower from the margin of the umbel. 

 The corolla is enlarged and irregular, thus adding to the conspicuousness 

 of the inflorescence. D, corolla partially removed to show the epigynous 

 character of the flower and the cushion-like nectary at the base of the styles; 

 0. ovary. E, fruit splitting into two nutlets. F, portion of hollow stem 

 with sheathing of leaf base. 



which has become a troublesome weed in pasture lands and mea- 

 dows. The calyx lobes are very small, a feature likely to be seen 

 in any epigynous flower. The incurved petals alternate with the 



