224 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



is f'or.cornod; l)iit as the diatoms would find their way into the stom- 

 achs of those animals only in connection with the grosser material 

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

 such as hap]-»encd to he mixed with or attached to their food. A 

 host of other forms, on or in the sea mud in that vicinity, would 

 therefore l)e missed entirel}^ 



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

 least to the last cruise just mentioned, made any special effort to 

 collix't the diatoms, in connection with its general gatherin^i- of other 



^......^..x ^,.,,^^^^j.^,^ 



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

 great im[)ortance of this work being tliorougldy carried on in the 

 future. The Diatomaceae are not only e([ually worthy of investiga- 

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

 ocean surfaces and beds, but they have a uni((ue value, shared by 

 no other forms, for determining important questions regarding the 

 extent and direction of occaii currents and the origin of tlie materials 

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

 cuiustances affecting the diatoms: The first is the indestructibility of 

 their siliceous remains; whence it rc^sults that, unlike most aquatic 

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

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

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

 siliceous parts of sponges. But, second, the diaLoms differ from these 

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

 port(Hl by even quite slow ocean currents or surface drifts from their 

 places of origin to remote points and fmally sifted down upon the sea 

 bottom. No other organism of pernument structure has any such 

 transportability. Botli of the foregoing facts, however, would be of 

 little im])ortanco for the pur])oses tnentioned were it not for the third 

 circumstance, that the Diatomaceae constitute an enormous group of 



somew 



om 



those localities on the land where the geological stratum in which 

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

 mt^thods of detrition, resulthig in carrying these forms into streams 

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

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

 there is a tropical, a temperate, and a frigid Ilora among tlie diatoms 

 as 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 tlie species found at the different stations would be, 

 foi- thes(> I't'asons, an exact means of tracing ocean currents, and in 



