SYMMETRY OF THE FLOWER. 355 
means rare ; while the trimerous is generally found in Mono- 
cotyledons, 
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 correspond 
in such particulars, while the parts of the gyncoecium are unequal 
to them ; as in Staphylea pinnata (fig. 788), where the three 
outer whorls are pentamerous, while the pistil is dimerous. The 
gyneecium 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 Crucifere, 
where there are four sepals, four petals, six stamens, and two 
carpels (figs. 25 and 26), 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, andreecium and gyncecium—are present, 
as in the Rue (jig. 611) ; where one or more of the whorls is 
absent, the flower is ticomplete ( figs. 29 and 30). When the parts 
of each whorl are uniform in size and shape, as in the Rue (jigs. 
579 and 611), the flower is regular ; under other circumstances 
it is irregular, as in the Pea (figs. 452 and 477). In a normal 
arrangement of the parts of the flower, the successive whorls 
alternate with each other, as shown in jigs. 785 and 787 ; 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 whorl ; 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 should be uniform in size and shape, and 
distinct from each other and from the surrounding whorls. This 
norma! and typical flower is, however, lable to various altera- 
tions, arising from several disturbing causes, which modify and 
disguise one or wore of their typical characters. Some of 
these causes have been already alluded to in the description of 
the different organs of the flower, but it will be necessary for 
us to investigate them more fully here, and classify for syste- 
matic study. All the more important deviations of the flower 
from its normal character may be arranged under the following 
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 
AAQ 
