484 PHYSICAL GEOGRAPHY. 



water, along with the name of the vessel and collector, and the date of 

 collection. 



The dust which collects at sea upon the sails or decks of vessels. This 

 kind of material, although not common, has been found to be of interest 

 when examined microscopically. It can generally be scraped up with a 

 piece of paper. When the quantity is so small that it cannot be col- 

 lected in this way, a piece of damp paper may be laid on it once or 

 twice, in several places, and then folded up before it becomes dry. Lati- 

 tude and longitude, direction of wind at the time of the falling of the 

 dust, name of vessel, date, and collector's name, should be noted on the 

 label. 



Recent gatherings of Diatomacecs. These are the most valuable, im- 

 portant, and rich of the gatherings containing diatomacese on which the 

 student depends for material for investigation, and they are so various in 

 character that it becomes difficult to give general directions that will 

 serve to indicate the modes of procedure to be followed in securing 

 them. To collect diatomaceae at all thoroughly, a considerable amount 

 of knowledge of their habits is necessary. In general, it may be said 

 that gatherings should be made of marine plants, or algae as they are 

 called, which grow entirely submerged beneath the water, attached to 

 rocks, piers, iron-, or wood-work. The dirtier such plants appear to the 

 naked eye, the richer will be the harvest of minute organisms secured, 

 as the brown coating, seen upon aquatic plants and similar submerged 

 objects, obscuring them, is but a mass of living diatomace^. The larger 

 and coarser algae, — more especially those having a slimy feel, — do not 

 usually yield many diatomaceae ; but the finer brown, red, or green fila- 

 mentous kinds are commonly covered with them. Detached fragments 

 thrown up upon the beach ought not to be kept if living ones can be 

 found, for they usually have had the diatoms rubbed off from them, and 

 are, besides, contaminated with sand. The living algje taken from their 

 attachment should be dried without washing or much compressing, and 

 may then be placed in layers, each specimen being plainly labelled with 

 the exact locality, date of collection, and collector's name. Fragments of 

 algae, which may break off from cabinet specimens, and would be rejected 

 by students of the algae, may yet be of value to the diatomist. Some of 

 the finest collections I have ever seen were derived from this source. 



