10 BOTANY PART I 



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

 nection between form and function often introduces jDhysiological 

 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 acquires an actual significance. 



Slightly differentiated structures, which are found at the beginning 

 of a series of progressively differentiating forms, are termed RUDI- 

 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. This term will not be 

 used, since by the use of the word " organ," it Avould 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 mainly deals with 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 O 



Plants show a great diversity in the form and arrangement of 

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

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

 ing the common origin of the homologous parts or members. 



The Development of Form in the Plant Kingdom 



The Thallus {^"). — When the body of a plant is not differentiated 

 into ^epaiatc mcmbei's, or is composed of members which (though they 

 may be similar) are not homologous with those of the most highly 



