,',S PHANEROGAMS. 



whorl ; and it was mentioned that the interposed whorl has sometimes not the full 

 number of members. These phenomena occur in various large groups of Dicoty- 

 ledons \ In Fig. 423 the five stamens of the decandrous flower of the group of 

 Bicornes which are interposed as a whorl of full number within the first whorl 

 are indicated by the lighter colour. The same is the case with the larger number of 

 Gruinales, among which however the Balsamineae possess only the typical five 

 stamens; the Linese and the genus Erodium have five additional rudimentary 

 stamens interposed between them ; while in Peganum Hannala and INIonsonia the 

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

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

 (Acerineae and Hippocastanese, Fig. 424) 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 Papilionaceae may be mentioned in addition, and among tetramerous ones 

 Q^nothereae, 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 



ric;. 425.— Diagram of Primulaceae. I'IG. 426.— Diagram of Vitis (Ampelidea-). 



superposed on the corolline whorl, as shown in Figs. 425, 426, and as occurs also 

 in the Rhamnaceae, Celastrinece, the pentandrous Hypericinege, and Tilia. Pfeffer^ 

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

 another and in acropetal order, while on the other hand in Primulacese 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 

 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. 427, 428) is complicated still further by the tendency 

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



' Payer's figures show that the interposed whorl, although of later origin, is sometimes exterior 

 to the typical whorl. The main point is that the position and number of die other parts of the 

 flower are exactly as if there were no interposed whorl. 



^ Pfeffer, Bot. Zeitg. 1870, p. 143; and Jahrb. fiir wissensch. Bot. vol. VIII, p. 194. 



^ Compare on this point what was said on p. 531. If the theory that is here objected to of the 

 flowers of Primulaceae is maintained, it is clear that the mode of expressing the floral formula must 

 then be altered, and the diagram be somewhat diffcrcnUy drawn. 



