350 ORGANOGRAPHY. 



By some writers, again, a flower is said to be s3TiimetricaI, 

 when it can be divided into two similar halves, as in Cruciferse, 

 where there are four sepals, four petals, six stamens, and two 

 carpels {figs. 419 and 420), and the whole so arranged, that 

 the flower may be separated into two equal parts. 



Various other terms are used in describing 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, androecium, and gyncecium are present, 

 as in the Eue {fig. 564); where one or more of the whorls is 

 absent, the flower is incomplete {figs. 423 and 424). "When 

 the parts of each whorl are uniform in size and shape, as in 

 the Eue {fig. 564), the flower is regular; under other circum- 

 stances, it is irregular, as in the Pea {fig. 461). In a normal 

 arrangement of the parts of the flower, the successive whorls 

 alternate with each other, as shown in figures 766 and 768 ; 

 thus here, the sepals alternate with the petals, the petals with 

 the stamens, and the stamens with the carpels. 



A perfectly normal and typical flower should possess a calyx, 

 corolla, androecium, and gyncecium, each of which should be so 

 arranged that its parts form but a single circle : the different 

 whorls should consist of an equal number of members ; the parts 

 of successive whorls should alternate with one another ; and the 

 organs of each whorl should be uniform in size and shape, and 

 distinct from each other and from the surrounding whorls. This 

 normal and typical flower is, however, liable to various altera- 

 tions, arising from several disturbing causes, which modify and 

 disguise one or more of the above typical characters. Some of 

 these disturbing causes have been already alluded to in the de- 

 scription of the different organs of the flower, but it will be ne- 

 cessary for us to investigate them more fully here, and classify 

 for systematic study. All the more important deviations of the 

 flower from its normal character may be arranged under the fol- 

 lowing heads : — 



1st. The adhesion or union of the parts of the same whorl; 

 or those of different whorls. 



2nd. The addition of one or more entire whorls in one or more 

 of the floral circles ; or increase in the number of parts of a 

 whorl, which is due to the multiplication by division of any or 

 all of the organs of a whorl. 



3rd. The suppression or abortion of one or more whorls ; or of 

 one or more organs of a whorl. 



4th. Irregularity produced by Tinequal growth,, or unequal 

 degree of union of the members of the same whorl ; or by 

 abnormal development of the thalamus or axis of the flower. 



That part of Botany which has for its object the investigation 

 of the various deviations from normal structure, both in the 

 flower and other parts of the plant, is called Teratology. 



