DICOTYLEDONS. 645 



number of stamens in the interposed and outer whorl is doubled. The order 

 ^sculineae is of special interest in this connection, since in some of its families 

 (Acerineae and Hippocastaneae, Fig. 455) the interposed staminal whorl remains 

 incomplete, so that the total number of stamens is not a multiple of the typical 

 fundamental number (five). Among pentamerous flowers Lythrarieae, Crassulacese, 

 and Papilionacese may be mentioned in addition, and among tetramerous ones 

 (Enotherese, in which a complete staminal whorl is interposed. 



One of the most remarkable deviations from the ordinary structure takes the 

 form in not a few families of Dicotyledons of the simple staminal whorl being 

 superposed on the corolline whorl, as shown in Figs. 456, 457, and as occurs also 

 in the Rhamnaceae, Celastrineae, the pentandrous Hypericineae, and Tilia. Pfeffer ^ 

 has shown that the two superposed whorls of Ampelideae arise independently of one 

 another and in acropetal order, while on the other hand in Primulace^e they first 

 appear in the form of five projections each of which forms a stamen, and from each 

 of which a petal subsequently grows outwards. In these cases we have no sufficient 

 ground for the hypothesis that an alternating whorl has been suppressed between 

 the two superposed ones ; although in other cases this supposition is justified, or at 

 least is very probable. Thus in the order Caryophyllineae, families, genera and 



Fig. 458.— Diagrram oi Scleranthus FiG. 459. Diagram of Phytolacca FIG. 460.— Diagram of Celosia 



(Paronychiacere). (Phytolaccaceae). (Amaranthaceae). 



species occur in which the corolla is absent and the stamens are superposed on the 

 sepals ; and since in the same natural group species also occur with a corolla, it may 

 be assumed that where the corolla is absent this is the result of abortion. The 

 diagram of these plants (Figs. 458, 459) is complicated still further by the tendency 

 which they exhibit to a de'doublement of the stamens and even of the carpels. 



When a flower has more stamens than sepals or petals, this may be the result, 

 as has already been mentioned, on the one hand of an increase in the number of 

 staminal whorls (as in Fig. 451), or on the other hand, of the interposition of 

 a perfect or imperfect whorl among the typical ones, or of de'doublevient of the 

 stamens (as in Fig. 458). These cases must be clearly distinguished from those in 

 which a larger number of stamens results from the branching of the original ones, 

 a phenomenon which is found in diff"erent sections of Dicotyledons, and is some- 

 times constant in whole families (see p. 544). Thus, for instance, in Dilleniaceae 

 (Fig. 461), Aurantiacese (Fig. 462), and Tiliaceae (Fig. 463), each symbol which 

 indicates a group of anthers corresponds to a single original stamen. In this case 

 the number of original stamens is the same as that of the petals and sepals; 



' Pfeffer, Bot. Zeitg. 1870, p 143; and Jahrb. fiir wissensch. Bot. vol. VIII. p. 194: (see 

 supra, p. 609). 



