1 74 Morphology under the Doctrine of [BOOK i. 



which idea no definition is actually given, though the whole 

 contents of the book are a search after a definition. We 

 may regard the idea of rejuvenescence, as presented by 

 Braun, as an extension of the idea of metamorphosis, in which 

 extended form it is adapted to take in even the results 

 of the cell-theory, of the history of development, and of the 

 modern knowledge of the Cryptogams from the idealistic 

 point of view. , One peculiarity of his mode of expounding his 

 views is observed here, as on other occasions, namely, that he 

 gives no precise and arbitrary definition to a word, for instance, 

 like rejuvenescence in the present place, and in a later work to 

 the word individual, but looks behind the word for a profound 

 or even mysterious meaning, which is to be perceived and 

 brought to light by contemplation of the phenomena. In 

 page 5 he says, ' Thus we see youth and age appear alternately 

 in one and the same history of development ; we see youth 

 burst through age, and by growth or transformation step into 

 the middle of the development. This is the phenomenon of 

 rejuvenescence, which is repeated in endless multiplicity in 

 every province of life, but nowhere appears more clearly 

 expressed or more accessible to investigation than in the 

 vegetable kingdom. Without rejuvenescence there is no 

 history of development.'- -' If then we ask for the causes of 

 the phenomena of rejuvenescence (page 7), we shall indeed 

 allow that nature, into which special life enters in its various 

 manifestations, excites, awakes, and works by the influences 

 which the years and even the days bring with them ; but the 

 true and inner cause can only be found in the desire after 

 perfection which belongs to every being in its kind, and urges 

 it to bring the outer world, which is strange to it, more and 

 more into complete subjection to itself, and to fashion itself in 

 it as independently as its specific nature admits.' Further 

 on he says (page 17), 'The impulse or tendency to develop- 

 ment in each creature is likewise no direction of activity 

 impressed from without, but one given from within and 



