84 ERYTHEA. 
follows: “Each form which, on comparative morphological 
considerations, is clearly less simple, or can be shown to 
have arisen by reduction or abortion of another type having 
the same fundamental structure, or in which a further 
differentiation and division of labor is found, will be 
regarded as younger, and as far as possible, and so far as 
other considerations will admit, will be reviewed later than 
the ‘simpler,’ more complete, or richer forms. For instance, 
to serve as an illustration: Epigyny and Perigyny are less 
simple than Hypogyny. * * Forms with united 
leaves indicate younger types than those with free leaves; 
hence the Sympetale come after the Choripetale, the 
Sileneee after the Alsinew, the Malvacew after the Stercu- 
liacew and Tiliacew, etc. * * * Of course, these princi- 
ples of systematic arrangement could only be applied very 
generally; for teaching purposes they have often required 
modification.” 
The mechanical execution of work is excellent and 
typographic errors are few. —M. A 
