XXX INTRODUCTION. 
of the several cases of malformation given in these 
pages are generally arranged according to their appa- 
rent degree of importance. ‘Thus, in a case of prolifi- 
cation associated with multiplication of the petals, the 
former change is a greater deviation from the customary 
form than the latter, hence reference should be made, 
in the first stance, to the sections treating on prolifi- 
cation, and afterwards to those on multiplication. To 
facilitate such research, numerous cross references are 
supplied. 
In the investigation of teratological phenomena con- 
stant reference must be made to the normal condition, 
and wice versd, else neither the one nor the other 
can be thoroughly understood. It cannot, however, be 
overlooked that the form and arrangement called nor- 
mal are often merely those which are the most common, 
while the abnormal or unusual arrangement is often 
more in consonance with that considered to be typical 
than the ordinary one. Thus, too, it is often found 
that the structural arrangements, which in one flower 
are normal, are in another abnormal, in so far that 
they are not usual in that particular instance. 
For purposes of reference, a standard of comparison 
is required ; and this standard, so long as its nature is 
not overlooked, may, indeed must be, to some extent, 
an arbitrary one. Thus in the phanerogamous plants 
there is assumed to exist, in all cases, an axis (stem, 
branches, roots, thalamus, &c.), bearing leaves and 
flowers. These latter consist of four whorls, calyx, 
corolla, stamens, and pistils, each whorl consisting 
of so many separate pieces m determinate position 
and numbers, and of regular proportionate size. 
A very close approach to such a flower occurs 
