General Conclusion 505 



animals. There is one protoplasm, and though the needs 

 of different organisms demand very varied ways of sup- 

 porting it, and though they call for different degrees of 

 development of its fundamental properties and powers, its 

 essential features are always the same. Its supplies of 

 food, its manner of nutrition, its relations to supply, 

 distribution, and expenditure of energy, and its power of 

 appreciating its relations with its surroundings, are at the 

 bottom characteristic of all apparently different cases. 



Though this stands out as a great result of the century's 

 work, many stages of its discovery may be thought worthy 

 of individual emphasis. The researches on the metabolism 

 of the plant made by Sachs in the early years of our period, 

 continued by Boussingault, Winogradsky, Lawes and Gil- 

 bert, Hellriegel and Wilfarth form very conspicuous con- 

 tributions to knowledge. The physical investigations of 

 Pfeffer and his pupils cleared up many obscure points in 

 the mechanical working of the plant. The demonstration 

 of the sensitivity of plants stands out as a remarkable 

 achievement and brings into great prominence the names 

 of Frank, Wiesner, and the Darwins. 



The wonderful advance in anatomical research presents 

 similar achievements. The establishment of the cell theory, 

 the elucidation of the law of the alternation of generations, 

 the discoveries connected with the nucleus with their 

 influence upon the problems of descent and heredity, were 

 all features of the period under review. The combined 

 influence of all these factors upon the principles of classifica- 

 tion and the problems of taxonomy led to profound dis- 

 content with the schemes of the older morphologists, and 

 affirmed without fear of contradiction that phylogeny is 

 the true key to classification. 



Another feature of the period was the spread of exploration 

 as well as of minute examination of structure and function. 

 It was not only spread, but systematized, and its results 



