668 POPULAR SCIENCE MONTHLY, 



The study of structure, whether macroscopic or microscopic, 

 leads one naturally to investigate the functions of the parts. The 

 study of functions is physiology, and since we have given up the 

 older notions as to the sacredness, the supernaturalness, of the 

 phenomena of life in favor of the more rational view that they 

 are chemical and physical, all physiologists to-day are pressing 

 forward, with chemistry and physics as their allies, to larger 

 knowledge and clearer ideas as to what constitutes life. Far as 

 we still are from a solution of the riddle of the ages, yet during 

 the present century progress hitherto unequaled has been made. 

 Animal and vegetable physiologists are now going hand in hand 

 toward their common goal. In studying the processes of nutri- 

 tion, growth, reproduction, and the phenomena of perception, re- 

 action, and exhaustion, they are supplementing one another. 

 There are indeed some few physiologists of training and disposi- 

 tion so broad that they decline to be known as animal or as vege- 

 table physiologists, but wish to be called what they really are, 

 students of the functions of living organisms and seekers after 

 light from Avhatever source upon life itself. The more one studies 

 the physiology of animals and plants the more one sees that the 

 distinctions which have been made between the two are more ap- 

 parent than real, and that as in so many other cases our names 

 are for convenience rather than for the exact expression of the 

 truth. 



The physiologist finds that there are two great classes of 

 plants : (1) Those which, able to obtain from the crude materials 

 of the soil and the air all the elements which they need for their 

 nutrition, lead self-dependent existences ; and (2) those which, 

 unable to elaborate their food from such matters, must get it from 

 other organisms, either directly or indirectly. All animals depend 

 ultimately for their food upon those plants which are able to 

 elaborate living matter from lifeless mineral salts, water, and air. 

 But there are quite as many plants which are as dependent as 

 animals. The groups of parasites, the flowering and the flower- 

 less, the dodders and many of the fungi and bacteria, for exam- 

 ple, are absolutely dependent upon living organisms, either ani- 

 mal or vegetable as the case may be, for their food. Other plants 

 extract from the dead and more or less decayed remains of organ- 

 isms the highly elaborated nitrogenous and carbon compounds 

 which are essential to all life. Still others are fairly independent, 

 but supplement their self-made food by other means ; for exam- 

 ple, the whole group of insectivorous plants and several of the 

 orchids. The saprophytic plants, those living on dead organic 

 matter, are very important in the economy of Nature. They 

 accomi:)lish rapidly, and with much less damage or offense to other 

 organisms, the decomposition of otherwise waste matters which 



