‘THE FL OWER 43 
It is evident that such a flower may be divided into two 
equal halves in several planes, for a line passing through the 
middle of any one petal cuts the | 
flower into two exactly similar parts. 
All flowers, however, are not so 
simple: sometimes where we should 
expect to find five stamens, only 
four are present. In cases of this. 
kind the place where we should 
expect to find the fifth stamen is 
sometimes indicated by some struc- 
ture; thus, in the figwort, where Fic. 45.—FLoran Diacram 
oF A Cyciic FLOWER 
only four stamens are present, the —(‘Tyrzp), showing WHORLS 
position of the fifth is indicated by oF Frorat Leaves ALTER- 
a distinct scale. (Fig. 123.) re ee 
In the dead-nettle the fifth stamen is also absent, but the 
position of the other four is such that it is easily seen where 
the fifth would be if it were 
not suppressed. (See Fig. 130.) 
The suppression of one or 
more parts and the unequal 
growth of others leads to differ- 
ences in the leaves of each whorl, 
and the flower is therefore irregu- 
lar. In the sweet pea, violet, fox- 
glove, dead nettle, the petals are 
not all the same size or the same 
shape: the corolla is irregular. 
Irregular flowers can be divided 


OF VIOLET, TRANSVERSE : eee . 
Section, Mzpian Pranz into two similar halves only in 
MARKED. one plane. A line passing 
The dot indicates the posi- 
tion of the stem. 
through the flower and the main 
stem represents the median plane 
of the flower; a line drawn at right angles to that the lateral 
plane. The sweet pea and violet can be cut into two equal 
halves along the median plane alone; this is the usual plane 
of the symmetry of the flower. : 
