FLORAL ENVELOPES. COROLLA. 



179 



from monopetalous (^f 376). In general, the corolla consists of several 

 petals, equalling the sepals in number, or being some multiple of 

 them. When this is the case, the floral envelopes are said to be sym- 

 metrical; when, however, by the abortion of some of the petals the 

 numbers do not correspond, then the flower becomes unsymmetrical. 

 When alluding to the general symmetry of the flower, the various 

 changes produced by some petals being undeveloped will be considered. 

 A corolla is dipetalous, tripetalous, tetrapetalous, or pentapetaloits, 

 according as it has two, three, four, or five separate petals. 



376. The general name of polypetalous (vohv;, many), is given to 

 corollas having separate petals, while monopetalous or gamopetalous 

 (ftwof, one, and ya^o?, union) is applied to those in which the petals 

 are united. This union generally takes place at the base, and extends 

 more or less towards the apex ; in Phyteuma, the petals are united at 

 their apices also. In some polypetalous corollas, as that of the Vine, 

 in which the petals are separate at the base, they adhere by their 

 apices. That a monopetalous corolla consists of several petals united, 

 is shown in such cases as Phlox amcena, some specimens of which have 

 the petals more or less completely disunited, while others exhibit the 

 normal form of coherent petals. When the petals are equal as regards 

 their development and size, the corolla is regular ; when unequal it is 

 irregular. Even although the separate petals are oblique, still, if they 

 are all equally so, as in many Malvaceaa with twisted aestivation, the 

 corolla is regular. The size of the corolla as compared with the 

 calyx, the number, direction, and form of its parts, and their relation 

 to the axis of the plant, require attention. * 



377. When a corolla is monopetalous, it 

 usually happens that the claws, or the lower 

 parts of the petals, are united into a tube 

 (figs. 287 t, 288 i), while the upper parts are 

 either free or partially united, so as to form a 

 commom limb (fig. 287 I), the two portions 

 being separated by the faux or throat, which 

 often exhibits a distinct contraction or ex- 

 pansion. The number of parts forming 

 such a corolla can be determined by the 

 divisions, as by the number of teeth, 

 crenations, fissures, or partitions ; or if, as 

 rarely happens, the corolla is entire, by the 

 venation. The union may be equal among 

 the parts, or some may unite more than 



Fig. 287. Regular monopetalous or gamopetalous tubular corolla of Spigelia marylandica. 

 c, Calyx, t, Tube of the corolla, /, Limb of the corolla, *, Summit of style and stigma. 



Fig. 288. Irregular gamopetalous or monopetalous corolla of Digitalis purpurea, or Foxglove, 

 c, Calyx. /), Corolla, t, Tube. I, Limb. 



