DEVELOPMENT OF PLANTS 



417 



has been referred to as a primitive form of the calyx (Fig. 298, 

 B, pr) and when present in the pistillate flowers it adheres to 

 the ovary (Figs. 298, E, pr; 300, B, pr). The pistils are pro- 

 vided with long delicate stigmas and are compound, containing 

 several ovules but only one usually matures. The wall of the 

 ovary develops into a tough coat about the seed, forming a fruit 



Fig. 298. Flowers and fruits of the birch family, order Fagales: A, in- 

 florescence of hornbeam {Carpinus) — s, staminate ament; p, pistillate anient. 

 B, staminate clusters from ament of alder (Alnus), each flower consisting 

 of four stamens attached to a four-parted perianth, pr. C, upper view of 

 the same cluster, showing the numerous bracts associated with the flowers. 

 D, fruit of Carpinus attached to the greatly enlarged three-lobed bract. D, 

 fruit cluster of hazel (Corylus) — b, bract encircling the ovary and within a 

 more delicate bract, pr, adnate to the ovary; s, stigma. F, fruit of Corylus, 

 the bract, b, in E has grown out into a tubular beaked structure that com- 

 pletely envelops the nut. 



known as the nut. Certain bracts of the flower increase greatly 

 in size as the ovary matures and form a conspicuous part of the 

 fruit. Thus in the hornbeam (Fig. 298, D), one of the bracts 

 develops into a large, three-lobed green leaf, in the hop horn- 



28 



