178 Dr. Hooker's Flora Antarctica. 



was covered with a stratum of pure white or green mud, com- 

 posed principally of the siliceous cells of Diatomaceae. These, 

 on being put into water, rendered it cloudy, like milk, and took 

 many hours to subside, * * * l 



"Scattered on the surface of the ocean, the Antarctic Diato- 

 maceae were seen connected in filaments, or resolved into the 

 simple frustutes of which they are composed. When entire, they 

 showed no signs of motion or irritability. The grumous or gran- 

 ular contents of the cells were yellow under the microscope ; but 

 in most the same species assumed an orange-brown, or burnt 

 sienna color, the intensity of which depended on the denseness 

 with which they were packed together. 



" The various means employed for selecting the species varied 

 according to circumstances, as the following enumeration of the 

 processes pursued will show. 1. Sea water was filtered through 

 closely woven bibulous paper (filter paper), which latter was fold- 

 ed, dried, and carefully put away. If a certain measure of water 

 be always thus treated, an approximate knowledge of the abun- 

 dance and scarcity of the various species and genera occurring at 

 different positions maybe gained. 2. The scum of the ocean 

 almost invariably contains many species entangled in its mass; it 

 was preserved in small vials, well secured. 3. A tow-net of fine 

 muslin, used when the vessels' rate does not exceed two or three 

 knots, secures many kinds, which may be washed off the muslin 

 and collected on filter paper. 4. The stomachs of Salpa and 

 other (especially of the naked) mollusca invariably contain Dia- 

 tomaceae-, sometimes several species. , These Salpce were washed 

 up in masses on the* pack-ice, and in decay they left the snow cov- 

 ered with animal matter, impregnated as it was, with Diatomaceae : 

 the reliquiae were preserved in spirits. 5. The dirt and soil of 

 the Penguin rookeries and especially their guano abound in Dia- 

 tomaceae, perhaps originally swallowed by salpae and cuttle fish, 

 which themselves become the prey of the penguins. 6. Ice 

 encloses Diatomaceae : they are deposited on the already formed 

 ice by the waves, or frozen into its substance during calm weather, 

 where the upper stratum of water rapidly congeals. Ice so form- 

 ed generally breaks up by the swell of the sea into thin angular 

 masses, which become orbicular by attrition, whence the name 

 pancake ice. The pancake ice was often seen a few hours niter 

 a calm, covering leagues of ocean, and uniformly stained brown 

 from the attendance of these plants. It was taken in buckets, 

 and when removed from the water appeared perfectly pure and 

 colorless. On melting, however, it deposited a pale red, cloudy 

 precipitate, excessively light, consisting wholly of Diatomacea 1 . 

 This precipitate was bottled on the spot, and proved more rich 

 in species than any of the other collections. The specimens 

 were also the best preserved : for Prof. Ehrenberg observes that 



