DEVELOPMENT OF PLANT PHYSIOLOGY 113 



through its union with animal physiology forms a debt which the 

 former is trying to pay to the latter, and which in part has been paid. 

 It was the recognition of heliotropic and geotropic phenomena in 

 plants which guided us to discovery of analogous phenomena in 

 animal organisms. And thus we see that the long-separated and 

 independently parallel disciplines have become united into a more 

 symmetrically developing general physiology. 



It seemed as if the doctrine of the cell, so important for physio- 

 logy, would have had a happier fate than all the other branches of 

 natural science. Its founders, Schleideri and Schwann, had worked 

 into each other's hands. Schleiden regarded this as a fortunate 

 circumstance, which, as he expressed it, "protected the doctrine of 

 cell-life entirely from the one-sidedness of a simply botanical or 

 zoological point of view." 1 But it has turned out otherwise. The 

 iron law of division of labor holds good here, also, and only after long- 

 drawn-out special researches in both fields has the conviction grown 

 upon us that experience in one field has something to teach us in the 

 other also. About half a century after the founding of the cell theory 

 the large results of animal histology worked a change. The happy 

 discovery of kar}-okinesis in the animal cell taught the botanists, 

 who saw their enlightenment near at hand in the study of plant cells, 

 in w r hich traces of karyokinesis had been seen, by means of the tried 

 methods of the animal histologist. From day to day the union of 

 plant and animal histology advanced, and our knowledge of the 

 organic elements gradually became more unified, the condition 

 which Schleiden held as an ideal, and, in company with Schwann, 

 had prepared for. 



In the field of botany, morphology and physiology sprang up 

 slowly side by side from the several above-mentioned foundations. 

 That we see at this time interrelations between them indicates a far 

 advanced condition. But this significant union is taking place by 

 no means without contention. There yet sticks in the heads of many 

 morphologists that these two parts of botany will thrive the better 

 the more completely they are separated from each other. Advan- 

 tageous as the division of labor has been, and as much as the study 

 of details has led to this, it must yet be clear to the far-sighted that 

 the solution of the great questions of plant life is possible only by 

 a morphological-physiological treatment. To express it roughly, 

 we may understand a machine when we take note not only of the 

 structure and form of its component parts, but also of their func- 

 tion and work; so may we get an intellectual grasp of the living 

 plant when we study its morphology in relation to its functions. To 

 make use of all demonstrable morphological facts in the explana- 

 tion of life processes is one of the most obvious phases of modern 



1 Schleiden, Grundzugederwiss. Bot., Vierte Aufl., Leipzig, 1861. Vorrede, p. xi. 



