272 THE AMERICAN MONTHLY [Oct., 



before, and the papers so used were put aside with the others in 

 a little sea water. The filtered water was then subjected to the 

 boiling point, and this was sustained for twenty minutes. When 

 cold, the water was divided equally in two jars, but in one of 

 them all the saved filter papers were washed. Both jars were 

 set in the window, and at the expiration of six weeks an in- 

 spection with the microscope was made. The jars containing 

 the clean water did not yield one diatom — and from the bottom 

 of the jar in which the filters had been washed, it required 

 many dips to be inspected before a Navicula could be got and 

 in all the examinations only one Amphora. Yet in both jars 

 the green uni-celled algse were found, intruders from the 

 atmosphere. The diatom spores, or germs were so minute 

 as to have passed through the filter paper almost entirely. I 

 queried— were these few spores thus retained by the filters larger 

 than those which had gone through ? At any rate the few dia- 

 toms these produced, so far as examined were of normal forms. 



Thus the conviction was forced upon me, that I was dealing 

 with diatom germs, or spores whose vitality had been sustained 

 in darkness through sixteen years. Hence it was a surprise to 

 me that my friend the late Dr. Wolle in his " Diatomaceae of 

 North America," p. xiii, could from my article make such de- 

 ductions as are contained m the following : 



" As regards the longevity of diatoms, * * * * they have 

 been known to survive even though kept for long periods in the 

 dark." 



" Bejiides reproduction by conjugation there is multiplication 

 by division ; and as diatoms do not grow these divisions tend 

 to make the resultant diatoms smaller and smaller, until some 

 become so minute, as in the Nilzschlae, Navicalae, and Amphorae, 

 that while living they can go through the pores of filtering pa- 

 per." 



The above I cannot but regard as a singular errancy of deduc- 

 tion — in a word, as contra-statements of three facts which ap- 

 peared to me to be warranted by my experiments. It was the 

 vitality not of the frustule, or plant, but of the germ or spore for 

 so long a period, and in an environment so adverse ; for prior to 

 cultivation not one living diatom was found by the microscope. 

 And certainly^ if from a germ or spore, the fission stage of the 

 diatom must be preceded by a growth stage, embryonic one 



