CHAPTER XIX. 
AMPLIFICATION AND REDUCTION. 
WHEREVER the attempt has been made by studying plants as they are 
seen living or fossil, to link them together into some coherent evolutionary 
story, theories of phyletic amplification and reduction have been freely 
employed. Sometimes greater prominence has been given to the one, 
sometimes to the other. 
The term amplification is used to embrace all changes leading to 
increased formal or structural complexity of the plant. It is necessary 
to distinguish between those changes of amplification which are indivi- 
dual and those which are phyletic. The former are the result of development 
traceable in some degree to the direct effect of external circumstances upon 
the individual organism: phyletic changes of amplification are those trace- 
able as inherited from generation to generation in an advancing stock. 
But in actual practice it is difficult to discriminate between them, for the 
two are not different in kind: in point of fact it is only on a basis of 
comparison that phyletic amplification can be recognised: it may indeed 
be held to be a perpetuation of such individual amplifications as are 
transmitted in descent. 
In the simplest cases amplification may be a consequence of mere 
non-localised distension of the plant-body; but in all more complex 
organisms growth is localised and continued at certain initial points, 
which thus take the character of apical cones, and define the polarity 
of the resulting structure. Or, furthermore, a secondary activity may 
appear in some intermediate zone, and new tissue be there intercalated : 
the common and obvious type of this is where increase in length or 
in width of the whole organ is the result, and that is what is usually 
understood as -intercalary growth. But it would also include those develop- 
ments of vascular tissue designated as secondary thickening. Closely 
associated with apical growth, but less commonly with intercalary growth, 
is the initiation of new apical points, which lead to the various modes 
of branching of parts. This has also played an important rdle in the 
origin of complex plants as we see them. 
