358 



ORGANOGRAPHY. 



is letramerous, and the symmetry, which is marked 4/, is quafer^ 

 vary, tetragonal, or square. The successive Avliorls in such a 

 flower may be comjiared directly with whorls of leaves, each 

 consisting of four organs; or indirectly with opposite decussat- 

 ing leaves combined in pairs, the internodes not being de- 

 veloped. When there are five parts in a whorl, as in Crassu/a 

 rubeuH (Jiy. 763), the flower is said to be pentavierous, and the 

 symmetry, which is marked thus, ^/, quuianj or pentagonal. 

 Such a flower may be considered as answering to the penta- 

 sticlious arrangement of leaves with the internodes undeveloped; 

 or to be composed of successive Avhorls of five leaves, the inter- 

 nodes between each Avhorl being almost undeveloped, or very 

 short. 



Of the above arrangements, the pentamerous is most common 

 among Dicotyledons, although the tetramerous is also by no 

 means rare; while the trimerous is generally found in Mono- 

 cotyledons. In Acotyledons, when any definite number can be 

 traced in the reproductive organs, it is commonly two, or some 

 multiple of that number. 



Although a symmetrical flower, as above described, neces- 

 sarily infers that the parts in each whorl are equal to, or some 

 multiple of one another, still it is very common for botanists 

 to call a flower symmetrical when the three outer whorls cor- 

 respond in those particulars, while the parts of the pistil are 

 unequal to them; thus in the Staphylea pinnata {fig. 766), 

 the three outer whorls are pentamerous, 

 while the pistil is dimerous. The pistil 

 of all the organs of the flower is that 

 which less frequently corresponds in the 

 number of its parts to the other whorls. 



By some writers, again, a flower is said 

 to be symmetrical, when it can be divided 

 into two similar halves, as in Cruci- 

 fera\ where there are four sepals, four 

 jjctals, and six stamens {figs. 421 and 

 422), but the Avhole are so arranged, that 

 the flower may be separated into two 

 equal parts. 



Various other terms are used in de- 

 scribing flowers, which will be best alluded to here, although 

 some have been previously noticed. Thus a flower is said to be 

 complete, when the four whorls, — calyx, corolla, stamens, and 

 ])istil are ])rcscnt, as in the Ihie {fig. 564), Iris, &c.; wliere one 

 or nmre of the whorls is absent, the flower is incomphte {figs. 425 

 and 426). When the ])arts of each whorl are uniform in size 

 and shape, as in tlic Hue (fig. 564), the flower is regular; 

 umler other circumstances, it is irregular, as in tiie Pea {fig. 

 463). In a normal arrangement of the jnirts of the flower, the 



Fiq. 766. 





Fi'o- 7fi(>. Dingrntn of Uie 

 flower of Staphylea pin 

 vata. 



