RELATION OP PLANT PHYSIOLOGY TO OTHER SCIENCES. 433 



identities between plant and animal life? To-day we know that plants 

 respire in the same sense and for the same purpose as animals; indeed, 

 the forms of respiration are the same in both kingdoms. Besides ordi- 

 nary respiration in which free oxygen is taken up, there is, in plants 

 as in animals, a so-called intramolecular respiration, in which fixed 

 oxygen in highly oxidized compounds serves to carry on respiration. 

 The newer investigation has acquainted us in no equi vocal way with 

 the power of motion — yes, even with the sensibility of plants. Slow 

 movements which are to be detected by change of position during 

 growth are common in plant life, but even very lively movements such 

 as are exhibited by swarming of certain reproductive cells (swarmspores 

 and spermatozoids) occur frequently in the lower groups of plants. 

 And shall one not speak of sensitiveness in plants when it is shown 

 that external influences such as light, gravity, etc., act as an irritaut 

 which the plant receives, conducts to parts more or less distant and 

 responds to by some definite movement or in general by some definite 

 reaction ? 



The principle of the division of labor has worked here as elsewhere 

 n the natural sciences, first separating and then bringing together. 

 Plant physiology has gone its own way, as has also animal physiology, 

 the one not concerning itself about the other; and only enlightened 

 minds have first discerned the inner identities of both, and felt them- 

 selves compelled in the solution of fundamental problems to reach out 

 for data into the apparently foreign territory of the other. Thus, one 

 of the greatest animal physiologists of the new era, Ernst von Brucke, 

 who once occupied this same place of honor, to which investigator we 

 are indebted for three great fundamental contributions in the field of 

 plant physiology. 



When investigation in each of the two fields had yielded a rich fund 

 of usable data and had placed them in an orderly arrangement, the 

 union of the two — plant physiology and animal physiology — began. 

 When one takes up a recent work on animal physiology he discovers 

 with satisfaction that already much consideration is given to the facts 

 and conclusions of plant physiology. Recently certain works upon 

 general physiology attest the natural association into which animal and 

 plant physiology have entered. 



The relations of physics and chemistry to plant physiology lie so 

 closely before us and are so well known that I need not here go into 

 nearer details concerning them. But that both these great fields of 

 investigation stand in reciprocal exchange with their younger sister, 

 plant physiology, I will illustrate by a characteristic example. One of 

 the foremost living plant physiologists investigated the working of 

 osmotic force in the life of a plant. He soon had to learn that, how- 

 ever much the physiologists had contributed to the knowledge of this 

 question, both in elementary and advanced works, it was not sufficient 

 for his purpose, and thereupon it was thought necessary by him to 

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