J JO PHANEROGAMS. 



are allied not only to those that are octamerous (like INIichauxia) but also to 

 those with dimerous whorls, among which CEnothereae may be especially men- 

 tioned. Of genera belonging to this family, Epilobium, for example, is constructed 

 on the formula S^^^ P^^ St^_^ C^, Circaea on that of S^ P^ S\ C^ ; and Trapa, with 

 the formula ^2+2 ^X4 '^''^4 ^2? ^^^^t also be included here. Although in Epilobium 

 and Trapa the calyx really consists of two whorls, this pseudo-whorl formed of 

 two decussate pairs is followed by the other whorls exactly as if it were a true 

 tetramerous whorl. But other dimerous and tetramerous flowers exhibit a more 

 considerable deviation from the type, inasmuch as the two dimerous perianth-whorls 

 which develope as if they were a tetramerous calyx or corolla are followed by a 

 staminal whorl which is superposed on the pseudo-whorl consisting of two decussate 

 pairs, as in Urtica and other genera of the order, and in Proteaceae with the 

 formula ^',^.2 Si^ C, (Fig. 339, p. 478). 



Among the dimerous and trimerous flowers of the orders Polycarpie and 

 Cruciflorae, where they are the most perfectly developed, a tendency prevails for 

 more than one whorl to go to the formation of the calyx, the corolla, the androecium, 

 and even the gynaeceum, a tendency which may be expressed by the formula 

 ^p(+p+...) ^pi+p+...) 'Sy^.(+p+...) C^,(+p4....); for example 



Fumariaceae, S^ P^j^^ -^^2+... ^r 

 Berberideae, 



Epimedium, S^^.-^ P^^.> Si^^^ C^ 



Berberis, ^'3+3 ^3^.3 Sl^^^ C^ 



Podophyllum, S^ P^^^^ Si.,\^ C, 

 Cruciferai, S^^^ P^, St,^^ C^^^,^). 



A large number of examples of this general formula are aftbrded by the 

 family IMenispermaceae, in which the whorls are sometimes dimerous, sometimes 

 trimerous, while sometimes whorls of each description occur in one flower; and 

 where almost every one of the organs may disappear by abortion \ 



In addition to the trimerous flowers already mentioned, there are also some 

 which come under the first-mentioned general formula S^ Pu •S^ni+u} ^« (-m) ; as, 

 for example. Rheum \\ith the formula S.^ P^ ^'4"+3 Q- Other trimerous flowers 

 again appear to belong to a third type, as Asarum with the formula -5'3 S/^a.^ C^. 



When the number of staminal whorls is considerably increased, it not unfre- 

 quently happens that the number of stamens in each whorl also undergoes 

 change, and complicated alternations arise. Flowers the structure of which is 

 otherwise altogether difl"erent resemble one another in this respect, as is shown 

 by the Papaveraceae on the one hand (Fig. 433), and by Cistineae and some 

 Rosaceas on the other hand. 



The reduction of the flower to a simpler condition is often carried so far 

 in many Dicotyledons (as in Monocotyledons) that each individual flower consists 

 only either of an ovary with one or several stamens, or, when the arrangement 



^ Eichler, Ueber die Menispermaceen, Denkschrift der k. bayer. Ges., Regensburg 1S64. — 

 Payer, Organogenie dela fleur, PL 45-49. — Eichler, Flora 1S65, Nos. 2-8 et seq. 



