446 PART IV. CLASSIFICATION. 



four or six leaves arranged in two whorls, consisting respectively 

 of two or three leaves. 



For purposes of comparative description, it is convenient to re- 

 gard each turn of the spiral in an acyclic or a hemic} 7 clic flower as 

 equivalent to a whorl : thus a well-defined series with f arrange- 

 ment would represent two whorls. 



As in the case of the foliage-leaves (see p. 9), so in that of the 

 floral leaves, the order of development is as a rule acropetal : hence 

 each whorl of the flower is developed later than the one external 

 to it, and earlier than the one internal to it. When, however, a 

 series of floral organs is becoming degenerate, its development is 

 retarded ; for instance, in the Compositse, Valerianaceae, and Um- 

 belliferse, the degenerate calyx is developed after the corolla, or 

 even after the androecium. The members of each whorl may be 

 developed either simultaneously or successively. 



In their arrangement, also, the floral leaves resemble the foliage- 

 leaves. When, in an acyclic or hemicyclic flower, the spiral is 

 continuous with the same divergence from one series of floral 

 organs to another, the members of the successive series lie on the 

 same radii drawn from the centre of the flower, that is, they are 

 directly superposed. A good example of this is afforded by the ter- 

 minal flower of the inflorescence of Berberis (Fig. 262 ; occasionally 

 in Epimedium, and also in Gagea among Monocotyledons), where the 

 stamens, petals, and sepals are all directly superposed. When, on 

 on the other hand, the divergence varies from one series to another, 

 direct superposition does not occur, but some form of alternation, 

 as is generally the case in acyclic flowers : for instance, the calyx 

 of certain (pentamerous) forms of Anemone and other Ramin- 

 culacese is arranged with a % divergence, whereas the divergence 

 of the stamens is y\ or T 8 T . In hemicyclic flowers with a simple 

 spiral perianth and cyclic stamens (e.g. Cannabinacese, Cheno- 

 podiacese), the stamens are superposed on the perianth-leaves. 



When the floral leaves are in whorls consisting of equal numbers 

 of members, the general rule is that the members of the successive 

 whorls alternate with each other : thus, in a flower with calyx, 

 corolla, androecium, and gynaeceum, each consisting of a single 

 whorl of five members, the petals alternate with the sepals, the 

 stamens with the petals, and the carpels with the stamens ; and 

 if radii be drawn from the centre of the flower, it will be seen that 

 the stamens are opposite to the sepals and the carpels to the petals, 

 or more briefly, that the stamens are antiscpalous and the carpels 



