RELATION OF PLANT PHYSIOLOGY TO OTHER SCIENCES. 439 



consumption of coal Deed lead to no disquietude, at least in so far as 

 there will be no diminution of oxygen in the atmosphere. 



I have dealt thus at length with this illustration, because I wished 

 through it to indicate to what false conclusions one-sided assumptions 

 and problematic suppositions can lead. The problem in question here 

 is much more complicated than is often supposed, even by prominent 

 scientists, and to the objections which I have already urged against 

 this doctrine of disaster very many more may be added, though it 

 must be said that the matter was never taken very seriously in 

 scientific circles. 



In the impulsiveness of its youth, natural science has framed still 

 many other one-sided suppositions when dabbling in strange territory. 

 Thus Liebig ascribed the downfall of the world-embracing Roman Empire 

 to the exhaustion of the soil, to the lack of phosphoric acid and potas- 

 sium in the cultivated land, brought about by " robber farming," i. e., by 

 too-continuous overcultivation of the soil. With propriety Du Bois- 

 Eeymond rejected this theory ; but, on the other hand, the historian could 

 not agree with this critic when he said: "lioman culture disappeared 

 because it was built upon the quicksand of aesthetics and speculation." 

 DuBois-Reyinond likewise attempted to solve a complicated phenome- 

 non by too simple a formula. 



Inadvertently we have just touched upon the relations of the natural 

 sciences to the mental sciences, especially of history. For a long time 

 these relations were very uncongenial, and insufficiency of knowledge 

 and narrow conceptions upon both sides have often enough led to severe 

 strife. The first attempts of naturalists to engage in the solution of 

 historical problems from their point of view, and of historians — I recall 

 here above all Buckle — to make use of natural history teachings in his- 

 torical research, did not turn out well, and on that account could 

 scarcely contribute toward an intellectual intercourse between the two 

 "camps," as they were referred to frequently in those times of strife. 

 It happened more frequently that these efforts suffered a severe rejec- 

 tion. So the saying was: "With the knife of the physiologist one may 

 not cultivate the hard soil of history, but to that end is needed the 

 strong plow of the historian." Or, an eminent historian relates that it 

 had been made clear to him that history could not permit itself to be 

 molested by Darwin and his associates. 



An eminent historical investigator who once occupied this place of 

 honor published very recently a work on genealogy. This, the author 

 himself said, built the bridge between the historical and the natural 

 sciences. In this work the effort is made to present systematically 

 genealogy as learning in all its various relations to historical, social, 

 political, judicial, and natural science questions. 



The animal physiologists as well as those of botany have busied 

 themselves not a little with the question of the determination of sex, 



