PREFACE TO THE FIRST EDITION 



To one interested in biology the study of i)hint anatomy 

 affords a rich and alluring field, since it reveals how plants, under 

 conditions the most exacting, have met and solved the problems 

 of their existence by achieving the power and habit of cell differ- 

 entiation and cell association into tissues adapted to carry on the 

 different physiological functions; and when the study of plant 

 anatomy is directed to reveal the process of cell differentiation and 

 the steps by which the mature tissues are made fit for their 

 functions, the student cannot fail to see at once its high biological 

 significance. 



The ontogeny and physiology of the tissues is in fact so illumi- 

 nating to their mature form and structure that the student of 

 anatomy works to a distinct disadvantage if he is not constantly 

 reverting for enlightenment to questions of origin and function; 

 and whatever motive may incite him to the study of plant anatomy, 

 whether it be purely intellectual curiosity, or the recognition of 

 the necessity of a knowledge of plant anatomy to the scientific 

 pursuit of pharmacognosy or agriculture, he will find the outcome 

 more worthy of his efforts if he has sought out the physiological 

 and ecological interpretation of his anatomical findings. It is 

 not nature's way to evolve cells and tissues at random, with no 

 problems to be solved by their evolution. The tissues are not an 

 aimless expression of the power of variability. Rather they 

 represent the means of the triumph of living organisms over the 

 conditions and forces which make up their environment. 



This book attempts to point out in a brief and elementary 

 way how plants arrive at this achievement by the evolution of 

 the different physiological tissue systems from a primitive, 

 undifferentiated embryonic tissue, and how the tissue systems 



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