viii PREFACE TO THIRD EDITION 



a continuous treatise. The omissions are palpable enougn, tor no 

 attempt has been made after encyclopedic writing. The material itself 

 is such as will be reckoned elementary. Elementary and fundamental 

 should be held as equivalent terms when applied to those facts and 

 principles upon which the Science itself is built : and it is to these 

 that the available space has been devoted. 



The book has not been written in conformity with the schedule of 

 work prescribed by any University or School : nor is it designed to 

 meet the requirements of any specified examination. Its object has 

 been to present a true picture in as simple terms as possible. Pro- 

 ceeding from the known to the unknown, it opens with a description, 

 structural and functional, of familiar Flowering Plants. The conse- 

 quent inversion of the evolutionary aspect of the Vegetable Kingdom 

 as a whole will probably be criticised. But a definite break has been 

 made at the end of Chapter XIX. Here follows a Chapter on " Evolu- 

 tion, Homoplasy, Homology, and Analogy." It is designed as an 

 introduction to the scientific comparison of Plants. The illustrative 

 material for this is then supplied by the description of a progressive 

 series of forms, starting from some of the simplest and proceeding to 

 those that are more complex. These have been selected in harmony 

 with general opinion as to the trend of evolutionary history. It 

 hardly needs to be said that those selected suggest only the barest and 

 most general outline by means of which the progress of Descent can 

 be sketched. Nevertheless they give a rational foundation, however 

 slender, for the generalisations advanced in Chapters XXXIII. to 



XXXVI. 



In preparing the text of this Third Edition, twenty years after the 

 first and thirteen years after retirement, I have had the advantage 

 of help from younger men actually engaged in teaching. The Chapters 

 relating to Physiology, viz. III., VII.-IX and parts of Chapter XI. 

 and XII., have been amended and largely re-written, and new figures 

 added to them, bv Dr. G. Bond, Lecturer on Plant Physiology in 

 the University of Glasgow. Professor M. Drummond of Manchester 

 University has revised the text of the Thallophyta at various 

 points, and has re-written Chapter XXXV., under the title of 

 Sex and Variation. He has also added paragraphs on Vitamins 

 to Appendix II., which deals with Vegetable Food-stuffs. In these 

 amendments we acknowledge valuable suggestions from Dr. F. W. 

 Sansome and Prof. I. M. Heilbron. To all of these I am deeply 

 indebted for their help. I have myself added short statements on 

 the Psilophytales and Equisetales, so as to aid comparison. And 



