596 APPENDIX A 



adaptive modifications to unlike modes of life. Thus among the closely 

 related oaks one species may be a large forest tree and another a spreading 

 shrub with underground stem, but both have very similar flowers and 

 fruit. The reproductive structures exhibit a wide variety of character- 

 istics — such as differences in number and arrangement of flower parts— 

 that are little affected by the environment and yet are so modified from 

 group to group and from species to species that they afford excellent 

 indications of relationship. 



Older and newer systems of classification. The conventional system 

 of plant classification, which we have used throughout this book on 

 account of its convenience and familiarity, divides the Plant Kingdom 

 into four great groups, called divisions, as follows: 



Division I. Thallophyta (algae and fungi). 



Division II. Bryophyta (liverworts and mosses). 



Division III. Pteridophyta (ferns and fern allies). 



Division IV. Spermatophyta (seed plants). 



For many purposes this scheme is still quite useful, but there has 

 been a growing tendency to break away from it in favor of some classifica- 

 tion that would more adequately represent plant relationships as they 

 are now understood. Various more modern classifications have been 

 proposed and some of these have gained wide acceptance. These new 

 classifications scarcely affect the groups of ordinal, or lower, rank in the 

 seed plants. The rearrangements have to do chiefly with the algae and 

 fungi, and with the higher categories throughout. The classification given 

 below largely follows the treatment in an excellent recent textbook, 1 

 except that we have adopted Trippo's proposal to use the same names for 

 the major categories as have long been standard in zoology. These are, in 

 descending rank: kingdom, subkingdom, phylum, subphylum, class, sub- 

 class, order, suborder, family, subfamily, genus, subgenus, species, and 

 subspecies. The extents of the older divisions are indicated, and the names 

 of extinct groups are starred. 



1 Hill, Overholts and Popp, Botany: A Textbook for Colleges, 2d ed., McGraw-Hill 

 Book Company, Inc., 1950. 



