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). 



