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THE AMERICAN NATURALIST [Vol. XLYIL 



Rosacea?, Caryophyllacea 1 , Cyperacea; and (Jramineae, the 

 floral type is very much more various both in number and 

 in relative position of parts. The evolution of the game- 

 tophyte from its gymnospermous to its angiospermous 

 condition is a continual progress from simple and vari- 

 able structures to those which are fixed and highly special- 

 ized. The same principle is evident as well among vege- 

 tative structures, for the lower and more "generalized" 

 families, both among conifers and dicotyledons, show a 

 greater diversity in their wood structure than do the 

 higher groups. 



This progressive evolution from a primitive variable 

 condition to one which is fixed and specialized is always 

 attended by a reduction in the number of similar parts. 

 Multiple structures are characteristic only of the lower 

 types of organization. Other characters tend to show a 

 similar phylogenetic change from the complex to the more 

 simple, with the result that a structure in its highly de- 

 veloped state is very often less complex than is its more 

 primitive homologue. Evolution more often involves 

 reduction than amplification. 



These four general principles of conservatism— that 

 there are definite categories of fundamentally conserva- 

 tive and fundamentally variable characters; that certain 

 organs or regions of the body are more conservative than 

 others ; that early stages in ontogeny are more constant 

 than later ones, and that advance in evolutionary de- 

 velopment involves an increase in fixity, are established 

 on a large and continually increasing mass of observed 

 facts and may well demand recognition from all biologists. 

 Many other principles, such as those concerned with re- 

 version and orthogenesis, are gradually being formulated 

 and it is only a matter of time and more extended observa- 



much more uniform and exact footing. 



To establish these laws on a sound basis of observed 

 facts is a matter of some labor, but it is a much less diffi- 

 cult undertaking than to provide a reasonably complete 



