BRACTS AND FLORAL LEAVES. 



corolla only are as a rule considered, e.g., the androecium and 

 gyncecium of a radially symmetrical flower may or may not agree 

 with the general symmetry. 



The floral receptacle, like the receptacle of a shortened flower 

 cluster, may exhibit considerable diversity of form (fig. 37). If 

 it is elongated, conical, or flattened, the flower is said to be hypo- 

 gynous, i.e., the androecium, corolla, and calyx evidently grow 

 from a region below 

 the gyncecium, or at 

 any rate do not start 

 from a higher level 

 (fig. 37, A). But the 

 receptacle may cease 

 growing at the centre 

 but not at the edges, 

 when it forms a cup- 

 like structure, on the 

 rim of which andrce- 

 cium, corolla, and calyx 

 are situated. Two con- 

 ditions are here dis- 

 tinguishable. Either 

 the gyncecium remains 

 free, and can readily 

 be dissected away from 

 the receptacle, or else 

 it becomes inseparably 

 fused with this. In 

 the former case (fig. 

 37, B) the flower is 

 termed perigynous, be- 

 cause the floral leaves 

 external to the gynce- 

 cium grow on a ridge round about it; in the latter (fig. 37, C), 

 epigynous, since they appear to grow upon it. Buttercup, rose, 

 and fuchsia are good examples of hypogynous, perigynous, and 

 epigynous respectively. 



In the buttercup, as we have seen, the perianth leaves are 

 arranged in ivhorls, and the stamens and carpels in a spiral. 

 Such a flower is called liemicyclic, because a part only of its leaves 

 are arranged in whorls (cycles). Departure from this type may 

 take place in two directions. On the one hand, an acyclic flower, 

 like the white waterlily, has all its parts in a spiral; on the 

 other hand, a cyclic flower has all its parts arranged in whorls, 

 as may be seen in stonecrop and white lily (fig. 38). 



F 



FIG. 37.— Kelation of Parts of Flower [after Prantl]. A, 

 B, C. diagrams of longitudinal sections of hypogynous, 

 perigynous, and epigynous flowers. Floral receptacle 

 dotted in A and B ; in C the inner half of dotted part 

 is wall of ovary, the outer half is receptacle ; ca. 

 calyx; co. corolla; an. stamens; <jn. pistil; ov. in- 

 verted ovule. 



