1 2 INTRODUCTION 



starch-containing endosperm cells can, if necessary, themselves under- 

 take the task of producing diastase, by an act of self-regulation. 

 Similarly uo one would venture to conclude that the animal stomach 

 lakes no share whatever in digestion, merely on the ground that the 

 small intestine can assume the digestive functions of the stomach when 

 the Latter is removed by operation. 



What has been stated concerning the method of extirpation, applies 

 essentially to all experiments that aim at suspending the function of a 

 given organ or tissue, even though the measures employed are less drastic. 



The comparative and the experimental methods are evidently of 

 equal value to the physiological anatomist as instruments of research. 

 Bach of these methods has its strong and its weak points, while neither 

 can claim to give more reliable results than the other in all circum- 

 stances. The investigator must test the value of both modes of enquiry 

 in every individual case, and he must as far as possible arrange his 

 work in such a manner that the two methods will mutually supplement 

 and control one another. 



This introductory chapter may fittingly conclude with a few remarks 

 concerning the history of physiological anatomy. Even the founders 

 of vegetable anatomy and physiology could not altogether fail to observe 

 that the various members of the plant body are endowed with special 

 functions. The protective function of epidermis and cork, the conduct- 

 ing capacity of vascular bundles, the absorptive activity of root-hairs, and 

 many similar relations, have long been matters of common knowledge. 

 The earlier work in this field, however, produced little more than a 

 mass of disconnected observations, which admitted only of the vaguest 

 generalisation; no methodical and exhaustive account of the connec- 

 tion between the structure and the functions of any tissue-system had 

 been written previous to the year 1874, when Schwendener published 

 his classical treatise on " The Mechanical Principles underlying the 

 Anatomical Structure of Monocotyledonous Plants" {Das mechanische 

 Prinzip im anatomischen Ban tier Monokotylcn), in which the definition 

 and diagnosis of a tissue-system was for the first time carried out con- 

 sistently in accordance with the principles now generally accepted by 

 physiological anatomists. The tissue-system selected by Schwendener 

 was that which constitutes the skeleton of the plant, and the structure 

 and arrangement of this " mechanical" system were by him brought 

 into relation with its function in the most convincing manner. 

 Schwendener's treatise not only raised the anatomico-physiological 

 tendency of plant-anatomy to the higher status of an independent 

 branch of research, but also opened the way for a novel demarcation 

 and classification of the various tissues with reference to physiological 

 conceptions. 



