360 



DICUTYLEDONES. 



There are two whorls of stamens, the external with introrse, and the internal 

 with extrorse anthers. The gynoeceum is often bi-carpellate (Fig. 354 D). 



The flowers may be considered as coustmcted upon the monocotyledonous 

 type. Pterostegia has a perfectly monocotyledonous flower with 5 trimerous 

 whorls. Rheunt likewise, bat here the external staminal whorl is doubled (Fig. 

 254 A). Oxyria has a dimerous Eftewm-flower (4-leaved perianth, 6 stamens, 

 2 stigmas). Rumex has a Rheum-Rower with the suppression of the internal 

 whorl of stamens (Fig. 354 Bj ; Ernex is a dimerous Rumex. Polt/gonum, to 

 which Coccolobn, Miildenbeckia and others are related, differs from Rheinu 



FIG. 355. Polygonum fagopyrwn : A branch with flower and fruits (nat. size) ; B flower ; 

 C the same in longitudinal section ; D anterior and posterior view of stamen ; E gynoeceum ; 

 F fruit (mag.) ; G fruit in longitudinal section; H transverse section, showing the curved 

 cotyledons embedded in the endosperm ; I the embryo. 



chiefly in having one of the leaves, which in the latter takes part in the forma- 

 tion of the perianth, developed in this case into a bracteole (so that the perianth 

 is reduced to five members), and several or all the stamens in the inner whorl 

 become suppressed. The perianth in Coccnloba and Miihlenbeckia is more or 

 less perigynous and becomes fleshy, enclosing the fiuit. Miildenbeckia 

 platyclada has flat branches with rudimentary leaves ; sometimes branches 

 with normal, arrow-shaped leaves are found. Atraphaxi*. 



