504 FLORA ANTARCTICA. [Fuec/ia, tie 



I must offer some apology for omitting a class of organisms which have been investigated, and considered 

 of vegetable origin, by Prof. Ehrenberg, and which are almost equally abundant in the Antarctic Ocean with the 

 Diatomacea, whether on the surface or at the bottom of the sea : these are the Pliytolitharia, Ehrb. I am not 

 aware of the precise limits of this Order, and of many of the genera composing it ; but from casual allusions, I 

 gather that the term Pliytolitharia is a conventional one, employed to designate the siliceous and other inorganic 

 particles, deposited in plants of a higher structure. Thus, Lithodermatium is a genus whose species are represented by 

 modifications of the siliceous epidermis of one or many species of JBquisetum ; and the Lithostylidia are the siliceous 

 cells of Graminea *. It is not my object to discuss in this place the expediency of constituting such orders, 

 genera, and species. The total absence of Equiseta from the Antarctic Flora, and of Graminem or other phsenogamic 

 plants from any position within 700 miles of Victoria Barrier where the PJiytolitharia abound, renders it in the 

 highest degree improbable that the latter should be of vegetable origin, f 



A few remarks on the phases and situations under which these curious vegetables occurred, will not be mis- 

 placed here, especially as I have little to add to what is already known of their habits and organization. 



Scattered on the surface of the ocean, the Antarctic Diatomacea were seen connected in filaments, or resolved 

 into thesimple frustules, of which they are composed. When entire, they shewed no signs of motion or irritability. 

 The grumous or granular contents of the cells were yellow under the microscope ; but in mass the same species 

 assumed an orange-brown, or burnt Sienna colour ; 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 cireurnstances, 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 folded, dried, and carefully put away. If a certain measure of water be always 

 thus treated, an approximate knowledge of the abundance and scarcity of the various species and genera occurring 

 at different positions, may be gained. 2. The scum of the ocean almost invariably contains many species entangled 

 in its mass ; it was preserved in small phials, well secured. 3. A tow-net of fine muslin, used when the 

 vessel's 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 Saljoa % and other (especially of the naked) mollusca, invariably 

 contain Diatomacea, sometimes several species. These Salpa were washed up in masses on the Pack ice, and 

 in decay they left the snow covered with animal matter impregnated, as it were, with Diatomacea : the reliunia 

 were preserved in spirits. 5. The dirt and soil of the Penguin Rookeries, and especially their Guano, abound in 

 Diatomacea, perhaps originally swallowed by the Salpa and Cuttle-fish, which themselves become the prey of the 

 Penguins. 6. Ice encloses Diatomacea : they are deposited on the already formed ice by the waves, or 

 frozen into its substance during calm weather, when the upper stratum of water rapidly congeals. Ice, so formed, 

 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 after a calm, covering leagues of ocean, and 

 uniformly stained brown from the abundance of these plants. It was taken in buckets, and when removed 

 from the water appeared perfectly pure and colourless. On melting, however, it deposited a pale red cloudy preci- 

 pitate, excessively light, consisting wholly of Diatomacea. This precipitate was bottled on the spot, and proved 



* See Ehrenberg, in Schrift. Berlin Akad., June, 1841. 



f Ou the contrary, I cannot but suspect that some of these PJiytolitharia are the remains of Crustacea, and 

 especially the siliceous (?) particles, which occur in the tunics of naked Jfollusca. 



J I do not remember to have examined the contents of the stomach of any Salpa between the latitudes of 

 the N. Tropic and the 80° S., which did not contain the remains of Diatomacea. Dictyocha aculeata was universally 

 found in the stomachs of those I opened when off Victoria Land. 



