464 SCIENCE PROGRESS. 



treats of the arrangement of tissues, but except for the 

 two main headings — primary arrangement and secondary 

 changes — there is little attempt at a natural grouping. 

 De Bary's book, while unrivalled as a storehouse of facts, 

 perhaps tends to leave on the mind of the reader the im- 

 pression that anatomy is after all nothing but an accumula- 

 tion of detail, and that a morphology of the tissues, based 

 on homology, and comparable to that of external organs, 

 does not exist. That this should be so is no reproach to 

 the author, who saw clearly that a scientific morphology 

 must be founded on development, and thought that the de- 

 velopmental data were too conflicting to form a satisfactory 

 basis for classification (1, p. 22). This difficulty still exists; 

 even now the attempt to found an internal morphology of 

 plants has only met with very partial success. The prob- 

 lem is of great complexity and will probably never be 

 completely solved. Still the attempt has been made, and 

 has given new life to the study of anatomy. 



It is to the French botanist Van Tieghem, more than 

 to any other individual, that the recent progress of internal 

 morphology is due. This statement involves no injustice 

 to the Schwendenerian school in Germanv, who have done 

 excellent service to anatomy, but from quite a different 

 point of view. The question which they have attacked is 

 that of the functions of the tissues, and the classification at 

 which they have arrived, as fully set forth, ten years ago, 

 in Haberlandt's Physiological Anatomy of Plants (2), is 

 purely physiological. Such a classification, though just as 

 important as a morphological one, is no substitute for the 

 latter (cf. Strasburger, 3). What we want, as morpholo- 

 gists, is to trace the homologies of the tissues, and to find 

 out, so far as we can, how the various forms and systems 

 of tissue have arisen in the course of descent. That they 

 have been modified at every step, and in every direction, 

 in relation to changing function, is obvious ; we cannot, 

 however, be content with an arrangement based solely on 

 the. functions which they happen to discharge at the present 

 stage of evolution. 



Van Tieghem's anatomical system is best understood 



