XX PREFACE. 



the original plan, and which is referred to more than 

 once in the text ; a separate treatment of this will the 

 sooner enable me to publish, with a certain degree of 

 completeness, my observations on the natural history 

 of various fresh-water Algae, in particular on many genera 

 belonging to the debateable region between the Veget- 

 able and Animal Kingdoms, as well as those that 

 produce active gonidia. 



After these remarks, which may explain the delay in 

 the appearance of these pages, I feel compelled to add 

 a word of justification in reference to the direction of the 

 researches which form the basis of the following obser- 

 vations, and which will doubtless be regarded in many 

 quarters as antiquated, and leading away from the strict 

 scientific path. A vivid conception of Nature, such as 

 is here attempted, which tries to find in natural objects, 

 the expression of living action, and not merely the effects 

 of dead forces, does not lead, as some think, to baseless 

 air-castles, for it does not set itself to study the life of 

 nature, in any other way than in its revelation through 

 phenomena ; and just as little does it exclude rigid in- 

 vestigation of the laws, governing all natural phenomena ; 

 for it is exactly by the investigation of the laws within 

 which, and the forces through which life acts, that it 

 hopes to arrive at a perception of what is given to life, 

 according to the difference of its stages. The justification 

 of the effort to comprehend all the phenomena of nature, 

 not only in their external reactions, but also in their 

 inner connection, as the data for an universal history of 

 living nature, lies in the very nature of the human soul, 

 in its connection, not merely external but inward and 

 essential, with living nature. As the study of nature 



