GENERAL BOTANY 



SECTION I 

 MOEPHOLOGY 



The object of vegetable morphology is the scientific study of the 

 forms of plants. It does not attempt to discover the causes of the , 

 development of specific forms, but rather has accomplished its purpose 

 when it succeeds in showing how one form may be derived from 

 another. The only real basis of morphological study is, accordingly, 

 the genealogical development or phylogeny (p. 1). As phylogenetic 

 development can only be inferred, and cannot be directly followed, 

 the methods of morphology must also be indirect. They are de- 

 pendent on the one hand upon ontogeny, i.e. on the study of the 

 development passed through by an organism in attaining its mature 

 condition, and on the other hand upon the comparison of existing 

 organisms with one another and with those that have become extinct. 

 To a certain extent the ontogenetic development of a plant repeats 

 its i^hylogeny and helps to elucidate the latter, while, by means of 

 comparative investigation, extreme forms may be connected by inter- 

 mediate links. As, however, the ontogeny of a plant is neither a 

 complete nor invariable repetition of its phylogeny, and as connecting 

 links between extreme forms are often Avanting, the results of morpho- 

 logical study are frequently incomplete. Such parts or members of 

 plants which it is reasonable to presume have had a common origin 

 are distinguished as homologous ; those which, while probably 

 having different origins, yet exercise the same functions, are termed 

 ANALOGOUS. Through the adaptation of different parts to the same 

 function, a similarity in both external form and internal structure 

 often results ; and in this way the correct determination of morpho- 

 logical relationships is rendered difficult. Only homologous parts 

 have the same " morphological value." lliis homology is determined 

 by the facts of phylogeny and origin, and not by any correspondence 

 in function. Though the function of any structure does not influence 



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