CHAPTER I. 



THE SCOPE AND LIMITATIONS OF COMPARATIVE 

 MORPHOLOGY. 



CONFRONTED with the great variety of plant-types which exist living and 

 fossil on the earth's crust, the Botanist may regard them in various ways 

 with a view to reducing them to some general conception of order. He 

 may be satisfied with the mere cataloguing and description of the 

 divers J forms which he is able to distinguish, and with the grouping of 

 those together which show characters in common : this is the work of 

 the Descriptive Botanist, and it naturally took the first place in the 

 historical development of the science. Or he may attempt to find in 

 such similarities of form as are shown by organisms thus grouped 

 together some consecutive account of their probable origin : this is the 

 work of the Scientific Systematist, or student of Phylogeny, and it is the 

 ultimate aim of all current Morphology. 



In the earlier periods the student of form understood himself to be 

 enquiring into the details of the Divine plan, as illustrated in a series 

 of isolated creations : and any similarities which species might show 

 would demonstrate for him merely the underlying unity of that plan. 

 But in these later days he believes that the comparative study of form 

 will lead him towards a knowledge of the main lines of descent. 

 Contributory to this, which can only result in a balancing of probabilities, 

 or often of mere surmises, is the study of the Fossils : Palaeophytology 

 gives the only direct and positive clue to the sequence of appearance 

 of plant-forms in past time upon the earth. Unfortunately the results 

 acquired as yet along this line of observation are so fragmentary that 

 they do not suffice to indicate even the general outline of the true 

 picture : they must for the present be used rather as a check to phyletic 

 theories than as their constant guide. The field is thus left in great 

 measure open to other lines of enquiry. 



A second line of evidence which bears upon the evolutionary history 

 may be derived from the geographical distribution of plants upon the 



