46 
although there are three external parts which are all 
alike, yet the three inner, which alternate with them, 
differ among themselves. This circumstance is of 
frequent occurrence ; that is to say, although general 
symmetry is observed, and the number of parts in 
one ring corresponds with those in another, yet the 
particular parts may be of unequal magnitude. When 
that is the case, the necessary equipoise is restored 
by a corresponding development in the other rings. 
For instance, if the front of one ring happens to be 
larger than its back, then in the next ring the back will 
be larscer than the front, and so on ; or some similar 
compensation will be discoverable, and the same mode 
of adjustment is observable in the two sides of any 
one separate organ. In the white Butterfly plant, 
for example, what is called the lip consists of two 
arms exactly like each other ; there is also a halbert¬ 
shaped central piece, with the two arms also like 
each other; the central piece is itself terminated by 
a pair of tendrils of exactly the same length, the 
same colour, the same breadth, and alike in all other 
respects. If divided lengthwise, the two halves 
would be precisely alike. Symmetry, therefore, is 
not in any degree lost, even in such irregular cases as 
that of the White Butterfly plant ( Phahenopsis ). 
92. It sometimes happens that the parts of a 
flower are unequal-sided. The rule for the parts of a 
flower is the same as that for leaves; if a line be 
drawn from the base to the point, through the middle, 
both halves should be alike. In the case of unequal¬ 
sided leaves, general symmetry is maintained by the 
larger and the smaller halves always bearing the same 
mutual relation to each other throughout the whole 
plant. The same thing occui'S in unequal-sided 
