the immensity of the problems before him; that he must 

 realize how fragmentary is the most advanced knowl- 

 edge of this subject. The foundation stone of physi- 

 ology is chemistry, and consequently its advance must go 

 hand in hand with the advance of that science; but there 

 is also, it must be admitted, the element of empiricism, 

 which is an unfortunate necessity in any branch of learn- 

 ing where any considerable mass of facts are not yet 

 correlated. The greatest advances are made in the direc- 

 tion of resolving this empirical information into more 

 compact and definite form, a task only possible by the 

 accumulation and correlation of great masses of data in 

 connection with the more definite information afforded 

 by chemistry or physics and more particularly modern 

 physical chemistry. It is plain, then, that we can never 

 go ahead of the data afforded by these sciences, but must 

 always follow somewhat behind them. It must not be sup- 

 posed, however, that physiology is in a nebulous condition, 

 despite the fact that we are but on the margin of the 

 unknown. Distinct and creditable advances have been 

 made since the days when the knowledge of plant mor- 

 phology and the chemistry of Lavoisier made possible any 

 reasonably satisfactory explanation of the functions of 

 plant organs. The establishment of a proper understand- 

 ing of how the plant obtains its food has been a matter of 

 the utmost importance, both from the development of 

 theoretical physiology, and from the standpoint of prac- 

 tical use. We know not only the definite chemical ele- 

 ments which are essential for plant life, but we know also 

 the quantity and form in which they are most favorable 

 for plant growth. Having established this, it is possible 

 to understand the role of plants in the general economy of 

 the world, and how their manner of life, in a broad sense, 

 supplements that of animals. There is also pretty definite 

 information as to the physical phenomena connected with 



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