196 EVOLUTION OF PLANTS 
with the Composite among the Dicotyledons, or with the 
grasses, which they far outnumber in species, they give 
the impression of a group of plants in a formative con- 
dition, which has not yet reached a stage which fits them 
to compete successfully with their hardier rivals. 
Among the interesting modifications shown by the 
orchids and not found elsewhere among the Monocoty- 
ledons (except in the nearly related Burmanniacez), is 
the adoption of the saprophytic habit by some of them. 
Such forms, e.g. Corallorhiza, are characterized by a 
partial or complete loss of chlorophyll, with a corre- 
sponding reduction of the leaves, which are small and 
scale-like. 
SUMMARY 
Considering the Monocotyledons as a whole, they are 
much less numerous than the Dicotyledons as well as 
simpler in structure, and these points together with cer- 
tain structural resemblances between them and the ferns 
seem to indicate that they are the more primitive of the 
two great divisions of the Angiosperms, and it is not 
improbable that they have originated directly from 
pteridophytic ancestors, or possibly through forms 
related to the Cycads. 
It seems likely that the lowest of the Monocotyledons 
are the simple aquatic forms like Naias, where the flower 
consists of a single stamen or carpel, and from these the 
higher types with hermaphrodite flowers, and later those 
with a showy perianth, have been derived. It is true that 
many botanists consider the extreme simplicity of the 
flowers of the aquatic Monocotyledons to be a reduced 
