HOOKER. — BOTANICAL INSTRUCTIONS. 05 



*' marine plants found in it. Sea-weeds are among the most 

 ** common of all bodies carried by currents near the surface or 

 " at various depths below, and from their nature are very likely 

 ** to be entangled and brought up." 



Carefully note and preserve Algae brought up in the dredge at 

 moderate depths, under 100 fathoms, or deeper. Preserve speci- 

 mens attached to shells, corals, &c., which would indicate their 

 being actually in situ. 



The following observations in the methods of collecting Diato- 

 maceae are extracted from the Flora Antarctica, vol. ii., p. 504, 

 and apply to Rhizopods and many other minute oceanic organisms : 



'* The various means employed for selecting the species varied 

 according to circumstances, as the following enumeration of the pro- 

 cesses pursued will show. I. 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. II. The scum of the ocean almost 

 invariably contains many species entangled in its mass ; it was 

 preserved in small phials well secured. III. 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. IV. The stomachs of Salpae and other 

 (especially of the naked) Mollusca, invariably contain Diatomacese, 

 sometimes several species. These Salpae were washed up in masses 

 on the pack ice, and in decay they left the snow covered with 

 animal mattter impregnated, as it were, with Diatom aceae ; the 

 reliquicB were preserved in spirits. V. The dirt and soil of the 

 Penguin rookeries, and especially their guano abound in Diato- 

 maceae, perhaps originally swallowed by the Salpae and Cuttle-fish, 

 which themselves become the prey of the Penguins. VI. Ice 

 encloses Diatomacese ; they are deposited on the already formed 

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

 v/hen 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 Avas taken in buckets, and when removed from 

 the water appeared perfectly pure and colourless. On melting, 

 however, it deposited a pale red cloudy precipitate, excessively 

 light, consisting wholly of Diatomaceae. 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 Professor Ehrenberg observes that some thus obtained appeared 

 as if still alive, though collected three years previous to his exami- 

 nation, and subjected to many vicissitudes of climate. The snow 

 sometimes falls on the surface of the still ocean-water and does 

 not freeze, but floats a honey-like substance, often called brash-ice ; 



