,i6 



NA TURE 



[August i, 1907 



duplicate, and all the duplicates were remarkably con- 

 cordant. The results were, that seeds in unheaiea earth 

 began to germinate on the ninth day, the total germin- 

 ation being 65 per cent. ; in earth heated to 250°, 150°, 

 95°, and 80°, no germination has occurred yet, although 

 twenty-two days have now elapsed, while in the case of 

 earth "heated to onlv do", germination did not occur until 

 the eighteenth day', and the total germination is only 

 30 per cent. 



Dr. Russell mentioned that in his experiments he had 

 not noticed anv retardation to be produced by the sterilisa- 

 tion of the soi'l ; but in his experiments, as well as in my 

 own with apple trees, no steps were taken to guard against 

 re-inoculation from the air, and such re-inoculation would 

 be very easy in the case of seeds just below the surface 

 of the soil. Another explanation may be that we have 

 not used siinilar seeds ; and from some experiments with 

 mustard, now in progress, it is evident that different seeds 

 behave differently, though the difference may be due to 

 the imperfect sterilisation of the seeds themselves in some 

 cases. Dr. Russell has been good enough to examine 

 my experiments whilst in progress, and I »believe that 

 he is satisfied with the results so far as they go at 

 present. 



There is not sufficient evidence yet to show whether 

 the bacterial action is a direct one on the seeds, or whether 

 it is an indirect one, as Dr. liiissell suggosled. modifving 

 some chemical change produced in the soil by heating. 

 The very low temperature (60°) which suffices to affect the 

 germination tells against the view that chemical change 

 is one of the governing factors, as also does the fact that 

 the results obtained with sand are similar to those obtained 

 with earth. On the other hand, it was found that with 

 soil which had been heated lo 150°, and then re- 

 inoculated, germination was much retarded, and was very 

 feeble, this pointing to soine chemical change which was 

 not counteracted at once by the re-inoculation. 



The view that plants in' growing charge the soil with 

 something which is toxic to other plants was put forward 

 a year or two ago by Dr. Whitney, but the evidence 

 adduced for it seems to have been very inconclusive ; the 

 details of Mr. Fletcher's results in (his direction will, 

 therefore, be expected with considerable interest. _ We 

 have, during the last three years, been endeavouring to 

 ascertain whether any action of this sort can account for 

 the effect of grass on trees, trees having been grown in 

 earth or sand in pots and watered with leachings from 

 earth or sand in which grass was growing. The results, 

 however, have been entirely negative. 



Spencer Pickering. 



cladocera — as well as vast numbers of rotifers, while the 

 smaller organisms form the food supply of the fish, which 

 occur in astonishing abundance, .'\lthough the tow-nettings 

 usually afforded a plentiful supply of the smaller animals, 

 they contained relatively little in the way of phyto-plankton. 

 Alga; were collected from the rocks and stones and the 

 submerged stems of plants, while the larger representatives 

 of the flora were also collected. 



The fish were for the most part obtained from the native 

 fishermen, and while some thirteen different species were 

 brought home, the overwhelming majority of those taken 

 belong 10 two species of the genus Tilapia. .'\ large speci- 

 men of the Nile perch {Lales niloiinis) was examined, 

 which measured 120 cin. and weighed 54 lb. Only a few 

 species of mollusca were found, with but a single lamelli- 

 branch amongst them, while the worms are represented 

 by certain small oligochaetes. The collection contains a 

 polyzoan with circular lophophore, while among the 

 hydrozoa, Cordylophora is found growing abundantly. 

 Perhaps the most interesting discovery is that of a medusa, 

 and the hvdroid form with which it is associated. W'hile 

 the water of the lake is now slightly brackish, there is 

 evidence that it was perfectly fresh even in historic times, 

 I so that the existence of this form here is rendered more 

 ! than ever remarkable. It is a typical anthomedusan. and 

 finds its nearest ally in the marine genus Sarsia. There 

 arc several animal groups apparently unrepresented in the 

 Birket el Qurun which we might well expect to find, since 

 they are common in the Nile, with which the lake is in 

 direct communication. Such are the crabs, prawns, and 

 sponges, of which no specimens were procured. Similarly 

 we obtained no examples of argulidae, leeches, or turbel- 

 laria. 



In addition to the actual collecting, certain physical 

 observations were made. The seiche alterations in water- 

 level appear to be very slight, as is only natural where 

 the greatest depth is but four or five fathoms. .\ number 

 of readings of the water temperature were taken which 

 prove unexpectedly interesting. The temperatures recorded 

 show a maximum of q^^-z in very shallow water close to 

 shore about 2.0 p.m., and a minimum of 54°8 as a surface 

 leading in the early morning. The difference between the 

 surface temperature and that of the water below may also 

 be very considerable, as was shown in one case by a differ- 

 ence of 8°.8 between the reading at a fathom and that at 

 the .surface. All these figures are doubtless explained by 

 the shallowness of the lake and the extremes of heat and 

 cold' to which it is often exposed. 



W. A. CiNNiNGTON, Christ's College, Cambridge. 

 C. L. BouLENGER, King's College, Cambridge. 



Biological Expedition to the Birket el Qurun. 



The lake in the Fayum province of Egypt known as 

 the Birket el Qurun has a very unique interest as the 

 remains of the historic Lake Moeris, which was used as 

 an artificial regulator of the Nile floods by the monarchs 

 of the twelfth dynasty. During the last few years a good 

 deal of attention has been paid to the lake and the whole 

 Fayum province bv Captain Lyons, F.R.S., and the staff 

 of the Egyptian Survey Department. No detailed examin- 

 ation of the flora and fauna had, however, been under- 

 taken, and it was lo furnish the desired biological 

 information that we were invited to make investigations 

 in the spring of this year. 



The Birket el Qurun is now reached with great ease 

 from Cairo, as the railway comes within a distance of 

 some seven miles. Consequently we had no difficulties of 

 transport to contend with, and began our work on the lake 

 shore on March 26. During a period of eight weeks we 

 made careful collections in a number of different parts of 

 the lake, and being provided with a sailing-boat of 

 moderate size we were able to make our way about by 

 water, camping in a number of likely places on the shore 

 sufficiently far apart. 



The lake seems lo be remarkable more for the quantity 

 of life which its waters contain than for the number of 

 different species inhabiting it. The tow-net revealed 

 immense swarms of cntomostraca — mostly copepods and 



NO. 1970, VOL. 76] 



The Atomic Weight of Cobalt. 



It has recently been suggested by Prof. J. J. Thomson 

 that the accepted atomic weight of cobalt, namely 59-0, is 

 probably too high, and that the true atomic weight of 

 cobalt is less than that of nickel. Prof. Thomson's 

 suggestion was founded on the results observed with 

 secondary radiation. 



We have made an attempt to determine the atomic 

 weight electrolytically by direct comparison with silver, 

 and obtain as the mean of fifteen determinations a value 

 of sTv for the atomic weight. 



We have also attempted to compare the atomic weights 

 of cobalt and nickel directly with each other and with 

 that of silver by placing three voltameters in series and 

 passing the same current through them, but on account 

 of unexpected difficulties due to secondary reactions in 

 the case of nickel we have not yet obtained satisfactory 

 results. 



We hope later to complete the investigation and give 

 details of the experiments. 



One of us (" F. H. P.") has also compared the absorp- 

 tion of cobalt and nickel for the $ radiation from uranium, 

 and the results indicate a smaller atomic weight for 

 cobalt than for nickel. 



F. H. Parker. 

 F. Pe.ike Sexton. 



Phvsical Laboratories, Woolwich Polvtechnic. 



