5419 INEQUILATERAL LEAVES. 
want of symmetry in their lobes. The Begonia is often cited as an 
example. The hickory, bean and poison ivy, may illustrate the 
same thing in compound leaves. In figure 100, ‘‘ The homologous 
parts a, b, c, d, while they are unlike one another, are, in their main 
proportions, severally like the parts with which they are paired. 
And here let us not overlook a characteristic which is less conspicu- 
ous but not less significant. Each of the lateral wings has winglets 
that are larger on the one side than on the other; and in each case 
the two sides are dissimilarly conditioned. Even in the several 
components of each wing may be traced alike divergence from 
symmetry, along with a like inequality in the relations to the rest ; 
the proximal half of each’ leaflet is habitually larger than the dis- 
tal half.” (Herbert Spencer, Principles of Biology, fig. 65, p. 31.) 
A. P. De Candolle says, “ This inequality generally exists only 
in alternate leaves, and I cannot find in my memoranda any ex- 
‘ample of an inequilateral opposite leaf. This fact tends to prove, 
that this inequality ought to be referred to the position of the leaf 
upon the plant favoring the development of one of its sides more 
than the other; and in this case, it is always the lower one which 
is developed most. This law is still more evident in the leaflets of 
pinnate leaves . . . . the side most developed is always the lower, 
_the upper being narrower and less prolonged. The same observa- - 
tion may be made upon the stipules, which are very frequently irreg- 
ular. In opposite leaves, there has been presented a curious exam- 
ple of inequality in Ruellia anisophylla ; — one of two opposite 
leaves is very small and narrow, and, as it were, abortive in com- 
parison with the other ; but symmetry is also met with in this irreg- 
ularity, for on comparing the successive pairs, the small leaf is 
found alternately on both sides. Stipules [sometimes] present 
analogous phenomena.” Seen 
Dr. Wilder has shown that « Elm leaves have the inner or up- 
per side much larger,” thus upsetting De Candolle’s theory that the 
inequality is due to the position of the leaf upon the stem. Vari- 
ous other reasons have been assigned for this inequality, all of 
which seem to fail when applied to numerous examples in their 
various stages of development. 
Schleiden believes that this want of symmetry is due to unequal 
pressure.in the bud. Spencer seems in doubt about the true 
cause, for he says, “ How far such differences are due to the po- 
sitions of the parts in the bud ; how far the respective spaces 
