300 THE AMERICAN MONTHLY [Nov 



the same by the aid of a small lens, the powder would 

 ignite and burn, nearly as freely as the fungus substance 

 known as "punk." By the aid of a spark produced in this 

 way, it would be possible to light a pipe or cigar in the 

 absence of matches. Further, these decayed woods al- 

 ways reveal something of interest in their cellular struc- 

 ture when examined as powder or splinters under the mi- 

 croscope. 



During my studies in May, having a living diatom-gath- 

 ering under examination, and knowing that I could, from 

 my supply, place in the field, a hundred or a thousand liv- 

 ing diatoms at a time ; it incidentally occurred to me to 

 mix a small quantity of the powder of decayed cypress 

 lying near at hand with the living motile diatom on the 

 slide. Acting on this thought, I discovered, that by the 

 aid of this decayed wood, everyone has it in his power to 

 study "ad libitum" every characteristic of motion associ- 

 ated with the Navicula species of diatoms. As all of the 

 larger forms, known as Navicula major ; N. nobilis and 

 N. viridis ; display all their motile functions in a similar 

 manner, they may be conveniently and agreeably follow- 

 ed under a magnification of two hundred diameters. This 

 permits a field for three or more diatoms to be observed 

 alternately or simultaneously, whereas under six hundred 

 diameters, one diatom would occupy most of the field and 

 multiply the efi"orts of the observer to retain it constant- 

 ly under study. 



In order to illustrate the manner of proceeding, we will 

 assume that there are some fifty or more Naviculae on the 

 slide, perfectl free from all other matter except possibly 

 some small rotifera), and that upon the slide there had 

 previously been put a minute layer of the wood-dust, just 

 such a layer as would adhere when the slide was turn- 

 ed over and tapped so as to dislodge such [)articles as 

 might not be in contact with the surface of the glass slip. 

 Uu beginning his observation, one would immediately 



