686 Transactions of the Society. 



If in the preceding pages one or other essay on this subject, 

 •which has appeared during the last decade, has not been mentioned, 

 I would ask indulgence on account of the seclusion of my place of 

 residence ; but I believe that no essential questions regarding the 

 subject have been overlooked. 



With this I conclude my work, and for the present, on account 

 of other studies, I take leave of a subject to which I owe many 

 pleasant hours of my Hfetime. Whether the text-books of botany 

 will take notice of the fi-uits of my investigation, or whether they 

 will adhere to the old mistakes, may be left to the future. Up to 

 the present I have only seen one work, the excellent synopsis of 

 botany by Leunis, newly edited by Professor Frank, which gives a 

 true account of the newest standpoint in these questions. 



Only by constant and persevering work can we expect further 

 progress ; it cannot be done by the mere purchase of expensive 

 immersion objectives. He who will only judge from a usurped 

 high position ; he who believes he can do something by setting up 

 diffi*action theories ; he who looks upon diatoms as aggregations of 

 crystals ; he who believes he can decide upon all sculpture questions 

 by observation of the surface ; he may keep to his own errors, but 

 he must not expect that I should answer his attacks which he has 

 based upon such means in order to find fault with my work, how- 

 ever learned may be his phraseology. Considering my positive 

 results, I must be excused in saying that I will not enter into dis- 

 cussion with such opponents. The literature of the last decade 

 furnishes so many cases where persons who, after their own more 

 or less special occupation with diatoms, look upon themselves as 

 important microscopists, bring to light the greatest imaginable 

 nonsense relating to sculpture questions. If I cannot indulge in 

 the hope of putting a stop to this by my present work, it will 

 no doubt contribute much for the intimate knowledge of these 

 interesting organisms, and when in future the structure of these 

 cell-walls is in question, the works of Pfitzer and Miiller will 

 not be exclusively referred to, but precedence will be given to 

 an investigator who ten years ago put the leading facts into 

 clear light. 



Lastly, I have to thank those scientists who sent me their 

 papers, ako Herr Moller, of Wedel, for sending various material for 

 investigation. 



EXPLANATION OF PLATES. 



All the figures have been drawn by the excellent 1/18-in. objective of Dr. Hugo 

 Schroder. All are magnified 1550, unless otherwise stated. The variety in tiie 

 amplification is due to the change of the eye-pieces and the alteration of the 

 correction-adjustment. They are, with the exception of fig. 7, no flighty 

 sketches, drawn after mere eye measurements, but all dimensions are based 

 on micrometrioal measurements. 



