10 BOTANY PARTI 



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

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

 its morphological value, the need of making clear the intimate con- 

 nection between form and function often introduces physiological 

 considerations into morphological questions. When, for phylogenetic 

 reasons, it seems possible to attribute to a number of different 

 members a common origin, such a hypothetical original form is 

 termed the fundamental or primitive form. The various modi- 

 fications which the primitive form has passed through constitute its 

 METAMORPHOSIS. In this way the theory of the metamorphosis of 

 plants, which was once but an ideal conception, acquires an actual 

 significance. 



Slightly differentiated structures, which are found at the beginning 

 of a series of progressively differentiating forms, are termed i;n>i 

 MENTARY ; imperfect structures, which have arisen as the result of the 

 deterioration of more perfect forms, are termed REDUCED. 



Vegetable morphology includes the study of the external form and 

 the internal structure of plants. The descriptive study of the external 

 form of plants has been termed organography ( 8 ). This term will 

 not be used, since by the use of the word " organ," it would seem to 

 have a physiological signification. Morphology takes no recognition 

 of the parts of a plant as organs, but treats of them merely as 

 members of the plant body. On the other hand, one of the most 

 important aims of physiology is to place the external form and the 

 internal structure of the living body in relation to the functions 

 performed by the latter ; physiology also investigates the causes of 

 the organisation. The study of the internal structure of plants is 

 often designated Anatomy or Phytotomy ; but as it usually includes 

 also the study of the more minute internal structure, it resembles 

 rather histology, in the sense in which that term is used by zoologists, 

 and concerns itself to a much less degree with the coarse anatomy of 

 the plant body. In any case, it is the simplest plan to designate the 

 study of the outer form EXTERNAL MORPHOLOGY, and that of the 

 inner structure INTERNAL MORPHOLOGY. 



I. EXTERNAL MORPHOLOGY ( 9 ) 



Plants show a great diversity in the form and arrangement of 

 their members ; it is the task of morphology to determine the points 

 of agreement existing between them. It seeks to do this by deter- 

 mining the common origin of the homologous parts or members. 



