ANGIOSPERMS. DICOTYLEDONS. 



459 



androecium and sometimes even the gynaeceum ; this is expressed by the general 

 formula, Sp(+p+ . .}Pp(+p + . .)Stp(+p+ . .) Cp(+p + . .); e.g. 

 Fumariaceae : 2 Pz + 2 St2 + . . Cz ; 

 Berberideae : 



Epimedium Sz-\- 2P2 + 2812 + 2d, 

 Berberis 63 + 3^3 + 3*9/3 + 3 Ci, 

 Podophyllum 6-3P 3 + 3 2 ^/3 3 + 3Ci; 

 Cruciferae 2 + 2^x4^/2 + 2 2 C2(+ 2). 



Many examples of this general formula are afforded by the family of the 

 Menispermaceae, in which the whorls are sometimes trimerous, sometimes dimerous, 

 sometimes even both dimerous and trimerous in the same flower, and in which 

 almost any one of the series of organs may disappear by abortion 1 . 



There are other trimerous flowers besides those already mentioned which come 

 under the general formula first proposed, SnPnStn( + n) Cn ( m), as Rheum with 

 the formula 6*3 P$ St-f + 3 C% ; but there are others again which seem to belong to a 

 third-type, such as Asarum with the formula 3 St^ + 6 C6. 



If the number of whorls in the androecium is considerably increased, it often 

 happens that the number of members in the whorls is changed, and complicated 

 alternations make their appearance ; flowers of entirely different structure in other 

 respects agree in this point, as is shown by the Papaveraceae on the one hand, and by 

 the Cistineae and many Rosaceae (Fig. 404) on the other. 



FIG. 404. Arrangement of the stamens in some Rosaceae. / Agnmonia Eupatoria and Sibbaldia. II Agrimonia 

 odorata. Ill species of Potenttlla. IV Rubus Idaens (peculiar case), see p. 417. 



In many Dicotyledons, as in Monocotyledons, the simplification of the flowers 

 often goes so far that each consists only of an ovary with one or more stamens, or, when 

 the flowers are unisexual, of a single ovary or of one or more stamens, the perianth being 

 entirely wanting, as in the Piperaceae, or reduced to a cup-like structure, as in Populus 

 and the female flower of the Cannabineae, or to hair-like scales between the sporo- 

 phylls which represent different flowers, as in Platanus. Flowers of this kind are 



1 Payer, Organogenic, Taf. 45-49. Eichler, Bluthendiagramme, II, p. 139, where the question 

 hether the theory of abortion is applicable to this family is discussed at length. 



