March 14, 1895J 



NA TURE 



461 



to render assistance to the biologist of supreme imporlance. 

 ■" The amount and direction of the abnormality will he indicated 

 if this [abnormal] frequency-curve can be split up into normal 

 curves." Analysis would in this way give us information which 

 we could perhaps not even guess at. 



I agree with Prof. Karl Pearson that " resolution into two" 

 will be sufficient. The stress of natural seleci ion at any moment 

 must always be bciween the best and the ne.^ct best. 



J n tolerably simple cases I have no doubt that the result of 

 Prof. Karl Pearson's labours will be to throw great light on the 

 matter. In more complicated ones we must look for some disap- 

 pointment in view of " the great variety of solutions which may 

 be suggested " 'p. io6). And the tentative discovery ol "com- 

 ponent normal curves " seems likely to be fallacious (p. go). 



(14) I think it is important to insist that the importance ol Prof. 

 Weldon's present results has reference to the sta'^ilily pmb'em. 

 He is fully aware of Ihi? fact when he says that " they cannot 

 be expected to hold in cases of rapid change such as those 

 induced artificially by selecti ^n under domestication, or natur- 

 ally by rapid migration or oth' r |)henomena resulting in a rapid 

 change of environment." These will lead to abnormal fre- 

 quency curves. 



(15) A few remaining points in Prof. Weldon's paper deserve 

 some remarks. 



I entirely agree with him in minimising the value of " spor's " 

 in evolution. As ai;ainst Nageli and his followers, I see no 

 ground for believing in any innate progressive tendency in 

 organisms. When the organism is in stable relation with its 

 environment it will continue so indefinitely. That is the con- 

 clusion I deduce from the flora of Egypt, and other fac's which 

 have been cited of the same kind. Prof Webion seems to 

 me to have supplied this position with a mo>t im[)ortant proof 

 by establishing the "selective destruction" of variations ab- 

 errant from the mean specific form. When the environment 

 varies, stability is destroyed ; but it will be ultimite'y re- 

 established, though with a different centre, by the operation of 

 natural selection. The result is that the organism has under- 

 gone some permanent degree of change. As I conc-'ive the 

 process, it is one of continuous adju-tment of " slight " varia- 

 tions on one side and the other. But it is important to keep in 

 view that variation in the environment stimulates the variation 

 in the organism which supplies the ultimate material for adjust- 

 ment. That the amount of the adjustment at any moment i? 

 slight is not incompatible with its amounting to almost anything 

 we like in the aggregate, if sutficient time be allowed. We 

 might as well deny that a curve can be built up from its in- 

 finitesimal elements. 



The value in this respect of sports may be easily overrated. 

 It appears to me that generally, so to speak, they attempt too 

 much anil overshoot the mark. The improbal)ility of a casual 

 sport being exactly what is wanted to bring the organism into an 

 advantageous relation to the environment at any particular 

 juncture seems to me very great. That such a thing may occur 

 is not denied, Ijut it can har lly be more than a "fluke." 



(16) This is confirmed by the fact that in the vegetable kingdom 

 sports are rare, and they seem to have little power of holding 

 their own in competition. I instanced the cases of the occur- 

 rence of copper-colourtd and laciniate foliage in many trees, as 

 well as the occurrence of varieties with weeping and fastigiate 

 habit. It is well known that to some extent these are per- 

 petuated by setd. Put the existence of such forms would un- 

 doubtedly be transient if it were not for their perpetuation as 

 curiosities under cultivation. 



(17) In museums it is u.uil to attempt the representation of 

 the mean specific form. The association of str kingly aberrant 

 specimens is interesting and often suggestive. But I do not see 

 that they illustrate more than the possibilities of variation and 

 the fact that it may be disc mtinuous. 



(18) I placed upon the table plants of the feral type and of a 

 recent cultivated form of Cineraria ^ritnita from the Canaries. 

 The difference in habit and in the form and colour of the 

 flowers was enormous. This has undoui^tedly Iteen brought 

 about by human selection. As far as is known it ha-; been ac- 

 complished by the gradual accumulation of small variations. 

 The horticulturist has not troubled himself about the foliage, 

 which, though more luxuriant, has remained jiractically un- 

 changed, liut it must not be assumed that it is unchangeable. 

 In the case of the Chinese primrose, the feral form fro n north- 

 west China, for which we are indebted to Ur. Henry, has 

 palmatifid leaves rounded in outline ; but the distal lobes are 



occasionally lengthened out. The horticulturist, as a matter of 

 fancy, working on this, has now split the type into two races, 

 one of which has palmatifid and the other pinnatifid leaves. 

 ;\Iany botanists would, undoubtedly, if they did not know their 

 history, assign to such a dilTerent specific rank. 



(19) I am not sure that I quite understand Prof. Weldon when 

 he says that "the statistical method is the only one at present 

 obvious by which [the Darwinian] hypothesis can be experi- 

 mentally checked." In the first place, I should myself hardly 

 call it experimental at all. In the next place, though I ihink 

 it will throw important light on the stability problem, iu the 

 important cases where evolution is actually taking place, the 

 mathematical analysis appears to me to be beset with very great 

 difficulties. We must not, therefore, expect too much from it. 



(20) On the other hand, museums, as at present organised, do 

 not help very much the study of evolution. In the case of plants, 

 I doubt if herbaria will ever he able to present material in a 

 sufficiently compendious or complete form to be of much use. 

 The study, however, of extensive series of a few species of 

 insects ranging over the whole of a large geographical area, 

 such as Mr. Elwes has brought together in the case of butter- 

 flies, must, it seems to me, afford most important material for 

 future discussion. W. T. ThiselTON-Dyer. 



Royal Gardens, Kew, March lo. 



Do Plants Assimilate Argon? 



It is a well-known fact that some plants are able to assimilate 

 nitrogen from the atmosphere and form compounds. Noiv, as 

 argon cannot be induced — at least up to now — by any known 

 process ol inorganic chemistry or physical science to enter into 

 a combination with one or more of the known elements, it 

 occurred to me whether that peculiar power which produced 

 the cell is no? able to form combinations with argon. The ex- 

 periment to grow suita'ile plants in an atmosphere of pureargon, 

 or argon mixed with pure oxygen, on a bed of pure sand, &c. , 

 would easily settle the question. 



If ihis experiment has not yet been made, perhaps you will 

 find space in y^ur paper for the above few lines. 



Essen- Ruhr, March 6. E. Blass. 



The first thing is obviously to find whether there is any argon 

 in a nitrogenous vegetable ; and experiments are now nearly 

 completed in my laboratory to see if nitrogen obtained from 

 peas contains any argon. Similar experiments are being made 

 with nitrogen from mice. In a few days I shall know the results. 

 But this is, of course, on the assumption that the process which 

 liberates nitrogen also liberates argon ; and it is by no means 

 certain. It should be rememiered that argon and nitrogen 

 have absolutely no similarity, and that their occurrence together 

 in air is a pure accident, due to the inertness of both. 



March lo. W. Ramsay. 



The Measurement of Pressures in Guns. 



In a paper " On Methods that have been adopted for 

 Measuring Pressures in the Bores of Guns" (Report of the 

 Briti-h Association, 1894), Captain Sir A. Noble has remarked 

 that it seems to him " that there is no method so satisfactory, 

 depite its attendant labour, as that of making the projectile 

 write its own story" (p. 540). That might be sufficient for 

 smooth bore guns, where there was little or no friction in the 

 bore, but it is quie unsatisfactory when applied to ri/led gans, 

 and especially B.L. guns. 



The two methods of experimenting now in use employ the 

 pressure g-aii<;e and xiie chronogni/i/t, both of which we will, for 

 this occision, sup,)Ose perfectly accurate. The pressure gauge 

 measures directly the pressure of the powder gas P, the quantity 

 wanted. The chronograph will measure P, the same pressure 

 of the powder gas, minus F, the resistance offered to the motion 

 of the shot by the rifling, the friction of the driving-band, &c., 

 = P - V, where K is oiten very great. The difficulty i-. to see 

 how these t«o different processes can confirm one another, as 

 F is unknown and of great importance. 



The only satisfactory method of determining the maximum 

 pressure of powder gas at any point in the b >re of a riJleJ gun 

 is to measure it directly, by the pressure gauge, which requires 

 many precautions to be taken, or by some other more simple 

 method. F. Bashforth. 



Horncastle, March 9. 



NO. 1324, VOL. 51] 



