ANGIOSPERMS. 



359 



FIG. 284. Flower of Cypripedium Calceolus after 

 removal of the perianth// (see the text). 



the flowering axis 1 . Much more complicated is the mode of formation of the true 



gynostemium above an inferior ovary, as in the Aristolochiaceae and still more in the 



Orchideae, in which these unions and displacements of the parts of the flower are 



combined with the abortion of certain members. As the subject will be further 



explained in the appendix, it will be sufficient in this place to examine Fig. 284, 



which represents the flower of Cypripedium after 



removal of the perianth pp in A from the side, in 



B from behind, in C from the front ; f is the 



inferior ovary, gs the gynostemium produced by 



the adhesion of three stamens two of which a a are 



fertile and the third s a sterile staminode with the 



carpel, the anterior part of which bears the 



stigma n. In this case the gynostemium is entirely 



composed of floral structures which have coalesced 



together, namely of the basal portions of the 



stamens and carpels, both of which spring from the 



upper margin of the hollow torus which forms the 



inferior ovary f. (See below on the development 



and interpretation of the flowers of the Orchideae.) 



The size and shape of the stamens is often 

 different in the same flower ; in the Cruciferae, 

 for instance, there are two shorter and four longer stamens, in the Labiatae, two 

 shorter and two longer ; in these two cases the androecia are termed tetradynamous 

 and didynamous respectively; in 

 Centradenia they are not only of 

 different sizes but also differently 

 articulated, as is shown in Fig. 

 276 A and B. Supported by 

 the history of development and a 

 comparison of relationships of 

 number and position in allied 

 flowers we are even justified in 

 speaking of stamens without 

 anthers, that is, without that 

 which is physiologically their 

 characteristic mark. Thus in 

 Geranium there are two whorls of 

 fertile stamens, but in its near ally 

 Erodium the stamens of one of 

 the whorls have no anthers; 

 these sterile staminal leaves or 

 staminodes usually undergo further 

 changes, becoming unlike the 

 fertile stamens and often petaloid, 



FiO 285. Stages in the development of the flower of Lantium album. 

 I, II, III very young buds seen from above ; / after the formation of the 

 rudiments of the sepals s, II after the appearance of the petals/, /// after 

 that of the stamens st and carpels c. IV transverse section of an older bud. 

 s the tube of the gamosepalous calyx, / that of the gamopetalous corolla, a 

 anthers, n stigmas. Supper lip of the corolla with the'epipetalous stamens. 

 VI the entire mature flower seen from the side. 



1 [An elongation of this character below the gynaeceum alone is a gynophore, one below the 

 androecium is an androphore.'] 



