100 



MORPHOLOGY, OR COMPARATIVE ANATOMY. 



rally alike in the same circle ; but in didynamous stamens (two long aud 

 two short) there is an exception to this. Irregular gamosepalous calyces 

 and irregular gamopetalous corollas are met with in endless variety of 

 forms, in the majority of which there is a tendency of the component 

 organs of a whorl to associate together in two groups, front and back, so 

 as to produce a bilabiate condition, as in the corollas of most Labiatae and 

 Scrophulariaceas. Unequal degree of union of stamens produces the 

 diadelphous condition of many Leguminosae, and the still more irregular 

 polyadelphous condition in the Orange. These points will be further 

 explained in the next Sections. 



It may be repeated here, that the deviations from irregularity falling 

 under this head almost universally arise during the development of the 

 bud from its originally regular rudiments. 



Development of the Thalamus. Most flowers have only very 

 short or contracted internodes developed between the whorls ; that 

 is to say, the receptacle or thalamus is usually not lengthened. 

 Exceptions occur to this, however ; for in the Caper tribe we have 

 long internodes between calyx, corolla, stamen, and pistil. 



Fig. 174. 



Fie. 173. 





Fig. 175. 



Fig. 173. Section of a flower of S'lene, with an internode between the calyx (which is turned 



back) and the corolla. 



Fig. 174. Section of the flower of the Eose; the pistils seated in a hollow receptacle. 

 Fig. 175. Flower of the Maple (Acer'), with the petals removed, showing the stamens arising 



from an hypogynous " disk " or outgrowth from the receptacle. 



In Dianthus and SUene (fig. 173") there is a short internode between 

 the calyx and corolla, in Gentiana between the stamens and the pistil. 

 In the Rose (fig. 174) the receptacle is expanded into a cup, from the 

 inner walls of which the carpels arise ; and in Nelumbium the carpels are 

 immersed in a large fleshy receptacle. In many cases what is termed 

 calyx-tube is in reality a tubular prolongation of the receptacle, from the 

 edge of which the calyx, petals, and stamens arise. In the Paeony the 

 receptacle is raised up into a kind of cup or " disk " round the carpels, in 



