224 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM, 



is concerned; but as the diatoms would find their \\a\ into the stom- 

 achs of these animals onh in connection with the grosser material 

 on which they feed, the Forms thus secured would represent only 

 such as happened to be mixed with <>r attached to their food. \ 

 hosl of other forms, on or in the sea mud in thai vicinity, would 

 i herefore be missed entirely. 



\ our Government, so far as I can learn, has not, previously at 

 least to the last cruise just mentioned, made an\ special efforl to 

 collect the diatoms, in connection with it- general gathering of other 

 organic forms, 1 think it will be opportune to point out here the 

 great importance of this work being thoroughly carried on in the 

 future. The Diatomaceae arc not only equally worthy of investiga- 

 tion with other forms of plant and animal life as inhabitants of the 

 ocean surfaces and beds, but they have a unique value, shared l>v 

 no other forms, for determining important questions regarding the 

 extent and direction of ocean currents and the origin ^\' the materials 

 composing the sea bottoms. This comes from several peculiar cir- 

 cumstances affecting the diatom-: The first is the indestructibility of 

 their siliceous remains; whence it results that, unlike most aquatic 

 plant-, they are not subject to decay, those which were formed cen- 

 turies ago being as well preserved as those of this year's product. 

 This is also true of mhhc other organisms, as the Radiolaria and the 

 siliceous part- of sponges. But , second, the diatoms differ from these 

 in being a- a class of such extreme minuteness a- to he readily trans- 

 ported by even <|uite -low ocean currents or surface drifts from their 

 place- of origin to remote points and finally sifted down upon the sea 

 bottom. No other organism of permanent structure has any such 

 transportability. Both of the foregoing facts, however, would he of 

 little importance for the purposes mentioned were it not for the third 

 circumstance, that the Diatomaceae constitute an enormous group <u 

 plants containing somewhat above 4,000 well-known species. Many 

 of these are exclusively fossil, and. are therefore derivable only from 

 those localities <>n the land where the geological stratum in which 

 they occur crops out and is subject to "weathering" and other 

 method- of detrition, resulting in carrying these forms into streams 

 and rivers and finally into the sea. Other forms, fresh water a- well 

 a- marine, are peculiar to certain localities; and, in point of latitude, 

 there is a tropical, a temperate, and a frigid flora among the diatoms 

 ;i- well as among the phanerogams. So that when the siliceous re- 

 mains of these species are discovered on the sea bottom or in sur- 

 face gatherings there are trustworthy data available for determining 

 their place of origin and consequently the direction and extent of 

 the currents or drifts by which they were transported. A proper 

 tabulation of the species found at the different stations would he, 

 for these reasons, an exact means of tracing ocean currents, and in 



