Vertical hauls between surface and 45 metres depth were made with a measuring net, throughout 1934, at a position 5 miles S.W. of Plymouth Breakwater in circa 50 metres depth of water.The phytoplankton organisms were counted and also assessed from their content of plant pigments.A close relation was found between numbers of diatoms and their pigment contents after making allowance for the small size of three species.The phosphorus content of the phytoplankton was estimated on several occasions.The zooplankton organisms per cubic metre of sea were counted and estimations were made of their phosphorus content.The diatom population differed from that found in 1933, in which year the spring outburst was shorter but more intense, the sporadic summer outbursts were more intense, the autumn one lasted longer; and more phosphate was utilised by the plants during the first half of the year.

In the Celtic Sea, to the south of Ireland, water in some winters becomes sufficiently cooled and heavy to flow to the edge of the continental shelf and to run down the continental slope to a depth of several hundred metres. A theory of the phenomenon, termed ‘cascading’, has been developed. Three winters have been examined in detail.In February 1927 much water, heavy enough to cascade, was present in the Celtic Sea and also in the English Channel. A probable course and speed of the cascading water over the shelf has been established. Since there were few observations of salinity and temperature over or beyond the slope, and none of oxygen anywhere, the theory cannot be completely established on the basis of the 1927 observations, full though they were.

(Text-figs. 1-2)In the deep water of the eastern North Atlantic below 2000 m. the variations with depth of salinity, temperature, density, oxygen, phosphorus compounds and nitrate are quite small. By contrast the silicate content is doubled in a descent from 2000 to 4°00 m.The distinctive behaviour of silicate is revealed by diagrams ( Fig. 1) relating it to salinity, temperature, density and total phosphorus at station 2659 worked by R.R.S. Discovery II on 12 May 1950 (Armstrong, 1951; Cooper 1952, Table IV). The temperature-salinity diagram (Cooper, 1952, fig. 15, to 15°°m. only) suggests that between 1200 and 2000 m. we have to deal with simple mixing of the mean Gulf of Gibraltar and North Atlantic Deep waters. If silicate concentration were subject only to mixing processes the curves in Fig. 1 between these depths would be straight lines. They are not-consequently it would seem that solution of either particulate silica or of aluminosilicates may be occurring. As yet, clear interpretation is not possible. At least five hypotheses may be erected to explain, in whole or in part, the observed distribution: (i) solution of bottom deposits; (ii) solution of ' clay' and of silica in suspension; (ill) concentration by vertical partition; (iv) tundra drainage; (v) sinking of surface water. These are examined in turn. ' SOLUTIONOF BOTTOMDEPOSITSDiscovery station 2659 was near the continental slope, solution from which could have occurred. The results of Wattenberg (1937) and Koczy (1950), however, suggest that the converse process occurs, adsorption or chemical combination of silicate from the water into the material of the bottom or into hexactinellid sponges. SOLUTION OF 'CLAY' AND OF SILICA IN SUSPENSIONThe distribution may have come about by solutionof mineralsof terrigeneous origin. If this were so the content of aluminium should increase with depth in much the same way as does silicate, and a diagram relating silica in solution to aluminium in solution should approach a straight line.

The new species of Gammarus here described was first noted in 1931 by Prof. H. Munro Fox, to whom I am indebted for the opportunity of examining it. He found it in abundance in the Droitwich district, living in the brackish waters of the River Salwarpe near the town, in the Canal, and in Wyken Slough near Coventry.

IN the late spring of 1934 four experiments were started to determine how quickly inorganic phosphate may be set free from plankton. Samples of plankton caught in fine and very fine silk tow-nets were analy.:ed for phosphorus (Cooper, 1934) and aliquot parts were filtered on a silk dise having 200 meshes to the linear ineh. The plankton was then added to two litre samples of fresh outside sea water in Winchester quart bottles. In all cases the amount of plankton initially present in the sample of sea water was less than 3% of that added.In each experiment a sample of sea water untreated except for passage through butter muslin was kept as a control. The Winchester bottles, except in Experiment 1, were wrapped in black paper and all were stored in a cupboard away from light and shaken by hand at intervals. The mean temperature of the storage cupboard was about 14°C. in April, 16°C. in May and 19°C. in June. At suitable times 100 ml. portions were removed from the well-shaken bottle and analysed for phosphate in the usual way (Deniges-Atkins method), except that samples enriched with plankton had first to be filtered through Zsigmondy membrane filters (filtration time, 20 seconds). Even so after a few weeks the colour match with standards in the phosphate analyses on these filtrates was not too good and the analyses are less accurate than those on ordinary sea water. The worst samples to compare were those rich in plants. All results are recorded as mg. P. per cubic metre corrected, when necessary, for salt error.