THE EVOLUTIONARY HISTORY OF PLANTS 305 
without making an unduly long chapter. Briefly, it may 
be stated that the monocotyledons are the simplest and 
probably the oldest angiosperms; the dicotyledons are 
higher in organization and came later. The descent and 
various relationships of the families of dicotyledons can 
be discovered by the study of the flower, fruit, and seed 
better than by the examination of the vegetative organs. 
The entire pedigree of the several families cannot be 
represented by arranging the names of the families in a 
straight line. It is, however, in a general way, as indi- 
cated by the succession of families in the Flora which 
accompanies this book, the Willow Family being perhaps 
the oldest (of the more familiar ones) and the Composite 
Family the youngest. 
