REMARKABLE PROPERTIES OF ROOTS. 777 



those who use it ultimately come to think they have given an explanation of the 

 process, while really they have only stated it. This is especially the case with the 

 term " stimulus". What is a stimulus? From the present state of our knowledge 

 we cannot yet give a concise answer to this question, consequently explanations in 

 which this word is inserted, are, as explanations, incomplete. 



In these remarks there is no desire to depreciate the results obtained by the 

 combined efforts of so many indefatigable investigators of past and modern times; 

 on the contrary, we may regard the wealth of careful observations and sagacious 

 inferences which form the present platform of our knowledge, and which have 

 been generally reviewed in the preceding pages, with just pride and satisfaction. 

 But this pride must not blind us to the recognition of the fact that most questions 

 concerning the life of plants are as yet only at the commencement of their solution. 

 Much has been done, but much is still reserved for the future. 



" Manchen Flug wagt menschliches Wissen das doch 

 Kaum ein blatt aufschlägt in dem Buch des Weltalls." 



vni I 50 



