PRINCIPLES 



OF 



PLANT-TERATOLOGY. 



INTRODUCTION. 



The Evolution op Plant-organs. — One of the most 

 important departments of botanical study is that of 

 the evolution of the forms of plant-life. A particular 

 form which it is desired to investigate from this point 

 of view may be either that of the entire plant, of one 

 of its organs, or of one of its tissues. The present 

 work is mainly concerned with the phylogenetic 

 (evolutionary) origin of the organs of plants. The 

 chief problem to solve is : From what original organ 

 has this or that form or structure been derived in the 

 course of evolution, and what are the changes through 

 which it has passed in order to reach its present 

 condition ? 



Thk Threw Categories op Organs. — At an early 

 stage of the investigation it became clear to the 

 present writer that there can never have been, so far 

 as vascular plants are concerned, more than three 

 categories of organs* in the past from which all 

 modern structures have descended, viz., stem, leaf, 

 and root, and that even the first of these, viz., the 

 stem, does not really exist at all, so far as morpho- 

 logical origins are concerned, but is built up solely by 



* I. e. three main siiMivisions of the plant-body. 

 VOL. J. 1 



