206 BRITISH PLANTS 
nected family history, which can be expressed as a 
genealogical tree with many branches, whose stems and 
roots lie deep in the ages of the past, and upon the tips 
of whose final branches rest the flowers of to-day. . 
But although the general development has been one 
of advance along certain lines of specialization, some 
forms, as might be expected, show evidences of retro- 
gression—that is, after having advanced to a certain 
point, they have gradually gone backwards. This is 
generally the result of special modes of life. Many plants 
which now appear simple in form and structure have 
really been derived from more specialized ancestors. 
This is the case with the flowering water-plants and those 
plants which, like saprophytes and parasites, are de- 
pendent for their food on external sources, dead or alive. 
Flowers also show reductions. For example, many flowers 
which are now pollinated by the wind were once visited 
by insects, but that they are degraded is shown by the 
fact that, in many cases, traces are still found in them 
of their entomophilous ancestry (see p. 167). 
