INTRODUCTION 5 



It is often a matter of chance or of convenience which 

 determines whether a man shall study one organism or an- 

 other. Sachs,* who may be called the founder of modern 

 plant-physiology, has said that although plant-physiology 

 owes much to animal-physiology, yet animal-physiology is 

 being enriched by the results attained by plant-physiolo- 

 gists. The appreciation of the fundamental unity of the 

 aims and the results of animal and plant physiologists has 

 recently led to the publication of two books on general 

 physiology, f In such books the manifestations of life are 

 described and discussed in a broad way; for details one 

 must turn to the special treatises on the physiology of 

 animals and plants. 



Though the phenomena of life are the same in all organ- 

 isms, life manifests itself in special ways in different or- 

 ganisms, making some more favorable for the study of 

 special phenomena than others. For example, the manu- 

 facture of starch from carbon-dioxide and water, and the 

 formation of tannin and certain other by-products in nutri- 

 tion, are subjects in plant-physiology only, just as other 

 special functions, such as those of nerves and muscles, car- 

 ried out by extremely differentiated organs, and the circu- 

 lation in vessels, are subjects in animal-physiology only. 

 Again, it is more convenient to study on low, small, aquatic 

 plants and animals some of the effects of light than on 

 higher terrestrial organisms, but the comparison of higher 

 and more complex forms with the lower shows that the 

 effects are identical in kind if not in degree. For this rea- 

 son, and because no "one man can know all the parts of the 

 whole subject of physiology equally well, it must still be 

 divided. While the following pages will be devoted mainly 

 to the study of plants, the reader should bear constantly in 

 mind that, at the same time that there are special vital 



* Sachs, J. von. Lectures on the physiology of plants, English transla- 

 tion, by H. M. Ward, p. 650. Oxford, 1887. 



t Verworn, M. Allgemeine Physiologic, two editions. English transla- 

 tion, by Lee. General Physiology, New York, 1899. Davenport, C. B. 

 Experimental. Morphology. Parts I. and II., New York, 1897, 1899. Others 

 to follow. 



