380 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 1916. 



animal denizens of the sea as the Radiolaria are as immortal as to 

 their silica encasements as are the diatoms; but their larger bulk 

 and more massive construction precipitates them to the bottom, while 

 the diatoms are held in suspension like the finest dust for an indefi- 

 nite distance. When we add to these two qualities a third one, the 

 large number of well-defined species, diilering in kind according to 

 the parts of the world in which they are found, we see that the pres- 

 ence of these organisms in an ocean current, even thousands of miles 

 from land, will often indicate the direction, the extent, and to some 

 degree the speed of the current by which they are borne along. It 

 should be here stated as a factor in this problem that the diatom flora 

 of any part of the world is always peculiar to that locality, just as 

 the land flora varies at diiferent latitudes and on the different con- 

 tinents. Thus we have a north and south arctic, a north and south 

 temperate, and a torrid diatom flora, which are in strong contrast to 

 each other and which, wherever met with, indicate the place of their 

 origin. In the same way the fresh-water forms, which are poured 

 in large quantities into the sea by the rivers, are still more distinctive, 

 and each section of the coast of our continent has at least some of 

 these plants to be found nowhere else upon the earth. 



The student of these minute plants is constantly made aware of 

 this sharp distinction of the diatom flora of one part of the world 

 from that of the rest. Let us take some examples : A recent study of 

 some living material from the Hawaiian Islands yielded a large and 

 elaborately ornamented diatom, Biddulfhia imperidlis, and search 

 through diatom literature revealed this in an obscure monograph, 

 where it was recorded that it also had been found " at the Sandwich 

 Islands." Doubtless the locality of the original specimen was prac- 

 tically that of the one later found. Another species was named by a 

 Philadelphia diatomist as having been found in a gathering at Mag- 

 dalena Bay, Lower California, and marked as " very rare," The 

 writer subsequently found it to be very plentiful in a dredging of 

 the U. S. S. Albatross, and, by comparison with the record of the 

 original discovery, it was shown that the two localities were within 

 a mile of each other. The writer named a new species discovered in 

 the Arctic Sea, and subsequently, in a study of the dust collected in 

 pockets on the ice floes of the Arctic, this diatom was rediscovered ; 

 and on comparison it was found that the latitude and longitude of 

 the two were practically identical. Material secured by the Smith- 

 sonian Institution adjacent to the openings of the Panama Canal and 

 previous to its completion has yielded a great many remarkable 

 forms.. A rare species known as Pleurosigma spectabile occurs 

 abundantly in one of the gatherings. This was previously reported 

 by Prof, Grunow, of Vienna, as occurring along the coast of Brazil; 

 that is to say, it is a coastal, middle Atlantic diatom. An even more 



