November 28, 1907] 



NA TURE 



79 



possible to perpetuate il. The fern-leaved form is, it can 

 hardly be doubted, a reversion to an ancestral type which 

 has been perpetuated in other species, and this may also 

 be the case with the ivy-leaved form, though this is more 

 obscure. 



The races of CEnothcra which De Vries has raised are 

 nothing more than what a horticulturist would expect; and 

 it may be conceded that if such races could hold their 

 own in nature, distinct species might originate in this way. 

 But there is no evidence that they do ; and the probability 

 of iheir being able to do so is against them. QLnotheras 

 are pretty prolific where they occur, and so far as my 

 experience goes they keep true to type. 



Cultural mutations seem, as a matter of fact, to have 

 little, if any, capacity for holding their own in the struggle 

 for existence. I cannot call to mind a single instance of 

 one which has been successful, and even in cultivation 

 there is some reason to think that they are short-lived ; 

 but this is a point on which we are in urgent need of 

 carefully ascertained facts. One is told, for example, that 

 new varieties of the potato mostly cease to give satis- 

 factory results after a few years. This is, however, a 

 case of purely vegetative reproduction, and similar state- 

 Tnents are made about the sugar-cane, which it is now 

 hoped to regenerate bv seminal reproduction. I can 

 remember when potato-fields were covered with flowers and 

 subsequently with fruit. I suppose it was thought 

 antagonistic to tuber-production, as it probably was, and 

 sterile races were selected accordingly. Prof. Hildebrand 

 came to this country to study the subject, and I was able 

 to supply him with information which I had collected for 

 another purpose. 



There is practically nothing to add to what has been 

 said on the subject by .Asa Gray (" Darwiniana," pp. 338- 

 347). It is notoriously difficult to get hold of old culti- 

 vated strains of garden plants, and change of fashion 

 hardly seems sufficient to account for the difficulty. Gray 

 points out " that with high feeding and artificial appli- 

 ances comes vastly increased liability to disease, which 

 may practically annihilate the race." This has all but 

 happened to the hollyhock, and, left to itself, the Phyllo.xera 

 would have exterminated the vine in Europe. The exist- 

 ence of a species in nature implies a complicated adjust- 

 ment to the surroundings. It is not sufficient to launch 

 upon them a new form ; in order that it may hold its 

 own, the adjustment must be provided as well. It is by 

 no means alw-ays an easy thing to transfer a species from 

 one part of the earth's surface to another. The seed of 

 the Kerguelen cabbage brought back bv the Challenger 

 germinated freely at Kew, but not a single plant was 

 raised from the seedlings, which all succumbed to a 

 ubiquitous Peronospora. 



De Vries has done good service in directing attention to 

 the study of mutations, the nature' and origin of which 

 deserve the most attentive study. They graduate into 

 monstrosities W'hich are even more mysterious. It is 

 worth while directing the attention of those who are 

 interested in mutations to the material which exists in 

 Japanese horticultural books. Japanese taste in such 

 matters is widely different from European. In the case of I 

 the garden convolvulus (Ipomrea). which is pretty stable 

 with us, the Japanese have figured an extraordinary range 

 of variations which no one else would dream of preserving. 

 W. T. Thiseltox-Dyer. 



^\"itcombe, November o- 



The Winding of Rivers in Plains. 



Hrfore writing to N.^ture on the theory of winding 

 rivers, it would have been wiser for me to have had some 

 observations made as to the conditions of actual flow in the 

 field in different circumstances. It is possible that the 

 more complicated conditions which obtain in some places 

 render the simple theory only partially applicable. My 

 letter was immediately applicable rather to the flow in 

 Prof. James Thomson's simplified model, where the arti- 

 ficial stream had a wooden bed, and the tendency to silt 

 was indicated by short pieces of cotton pinned by one 

 ■end to the bottom. It may be that the deposit of drift 



NO. 1987, VOL. 77] 



on the inner side of some streams retards their flow 

 by an unexpected amount ; and probably there are other 

 causes which prevent the James Thomson theory from 

 being the last word on the subject. I do not pre- 

 tend to be a field naturalist in any sense, and my 

 cautionary note concerning the flow of glaciers I would 

 ask readers to apply to the flow of rivers also, and to 

 interpret the whole of my letter as a hint and exposition 

 of theory rather than as an assertion and statement of 

 fact. Oliver Lodge. 



November 20. 



Sir Oliver Lodge's letter in N.iture of November 7 

 on the winding of rivers in plains has induced me to 

 measure the velocity of flow in different parts of a bend 

 in the river Wey near here. A short line — 17 feet — was 

 measured on the bank at the bend, and marks set up at 

 right angles to it, and the time taken by blocks of wood 

 to move between the marks measured with a stop-watch. 

 The distances of the blocks from the inner bank were 

 estimated in terms of the breadth of the river, with the 

 following results ; — 



03 



o'S 



0-6 

 08 



Velocity in feet 



per second 



0-30 



0-45 



0-55 

 071 



This does not bear out his statement that " the flow is 

 most rapid on the inner or sediment-depositing side of the 

 bend," and that the water near the concave bank is 

 nearly stationary, but upholds the common opinion of 

 boating men and others. 



The numbers refer to the suriace flow only, and it is 

 quite probable that there may be the undercurrent across 

 the bed of the river ; in fact, the sudden shelving so often 

 noticed in rivers, and harbour channels where there is a 

 strong tide, has led me to suspect for a long time such 

 cross-currents. 



The surface flow-lines are neither parallel nor straight. 

 For this reason a short base line was used, and the 

 velocities obtained are only approximate, but are certainly 

 not far from the above values. 



.At the end of the experiments two blocks of wood were 

 simultaneously floated down the stream, one near the 

 inner, the other near the outer bank, and the latter won 

 the race by twelve seconds. 



However, I noticed that close to the outer bank (within 

 2 or 3 feet of it) there were back eddies forming a set of 

 feeble whirlpools, and these may play an important part in 

 the scouring. R. C. Slater. 



Charterhouse, Godalming, November 17. 



The Occurrence of Copper and Lithium in Radium- 

 bearing Minerals. 



It is possible that the remarliable action of radium 

 emanation on copper, as recently announced by Sir William 

 Ramsay (Nature, July 18, vol. Ixxvi., p. 269), may not 

 be confined to solutions, but may also occur in the solid 

 state. If so, it should be found that those minerals 

 which contain both radium and copper contain lithium 

 also. 



In connection with another investigation, I had 

 separated a sample of pitchblende, from Gilpin County, 

 Colorado, into its principal constituents. The amount of 

 copper in the sample was considerable. The final filtrate, 

 remaining after the separation of the various analytical 

 groups, contained only ammonium and alkali salts. After 

 the evaporation of a portion of this solution, representing 

 about 3 grams of the mineral, and the volatilisation of 

 the ammonium salts, a small residue was left which, 

 when examined spectroscopically, gave a very bright 

 lithium line. This result led me to examine four other 

 samples of uranium-radium minerals. These samoles com- 



