550 BOTANY PART n 



HYPOGYNOUS (Fig. 521, 1). If, however, the end of the axis is 

 expanded into a flat or cup-shaped receptacle (hypanthium), an interval 

 thus separating the androecium and gynaeceum, the flower is termed 

 PERIGYNOUS (Figs. 520 B, B', 521, 2). When the concave floral axis, 

 the margin of which bears the androecium, becomes adherent to the 

 gynaeceum, the latter is said to be INFERIOR, while the flower is 

 described as EPIGYNOUS (Fig. 521, 3). 



The regions of the axis, or of other parts of the flower which 

 excrete a sugary solution to attract the pollinating animal visitors, 

 are called NECTARIES. Their ecological importance is considerable. 



In a typical angiospermic flower the organs are thus arranged in 

 five alternating whorls, of which two comprise the perianth, two the 

 androecium, while the gynaeceum consists of one whorl. The flower 

 is PENTACYCLIC. The number of members is either the same in each 



FIG. 521. Flowers in longitudinal section. 1, Ranunculus sceleratus with numerous apocarpous 

 carpels on a club- shaped receptacle; hypogynous flower. (After BAILLON, magnified.) 

 2, Alchemilla alpina, perigynous ; 3, Pyrus Mains, epigyuous. (After FOCKE in Nat. Pflanzen- 

 familien, magnified.) 



whorl (e.g. three in a typical Monocotyledon flower, or five in a typical 

 Dicotyledon flower), or an increase or decrease in the number takes 

 place. This is especially the case with the whorls composing the 

 androecium and gynaeceum. Further, as is shown in the androecium, 

 a whorl may be entirely omitted or the number of whorls may be 

 increased. Flowers with only one whorl in the androecium are 

 termed haplostemonous, and those with two whorls diplostemonous. 

 When the outer whorl of the androecium (and in correspondence with 

 this the carpels) does not alternate with the corolla but falls directly 

 above this, the androecium is obdiplostemonous. 



A diagram (cf. p. 88) of a pentacyclic Monocotyledon flower, so 

 oriented that the cross-section of the axis of the inflorescence stands 

 above and that of the subtending bract (cf. p. 121) below, is given in 

 Fig. 522, and that of a Dicotyledon flower in Fig. 523. 



Both these floral diagrams are spoken of as empirical diagrams. A theoretical 

 diagram, on the other hand, is obtained when not only the organs actually 

 present are represented but also others the former presence of which must be 



