54 



NA TURE 



[November 17, 1892 



therefore, the leading English-speaking botanists who have 

 occupied themselves with systematic botany have been in 

 substantial agreement that the adoption of a strict law of 

 priority in nomenclature must give way to considerations of 

 convenience. 



Well known and accepted names are not therefore to be 

 lightly changed as the result of mere bibliographical research. 

 As to specific names the often merely mechanical process of de- 

 scribing a new species is held to be of little value compared with 

 the more difficult task of assigning to the plant described its true 

 affinities and correct systematic position. The principle which 

 guides Kew practice in this matter is laid down by Sir Joseph 

 Hooker in the preface to " The Flora of British India " (p. vii). 

 He remarks : — 



"The number of species described by authors who cannot 

 determine their affinities increases annually, and I regard the 

 naturalist who puts a described plant into its proper position in 

 regard to its allies as rendering a greater service to science than 

 its describer when he either puts it into a wrong place or throws 

 it into any of those chaotic heaps miscalled genera with which 

 systematic works still abound." 



The following paper on the subject deserves the wider circu- 

 lation which its reprint in Nature would give it. It repre- 

 sents the Harvard tradition and practice, and is the last scien- 

 tific utterance of Dr. Sereno Watson, who so soon followed to 

 the grave his illustrious predecessor, Asa Gray. 



Kew, November 14. W. T. Thiselton Dyer. 



On Nomenclature.! 



[It was the request of the late Dr. Sereno Watsoa that the following com - 

 munication, dictated by him in his last illness, should appear at an early date 

 in the Botanical Gazette. — Eds.] 



For some time I have had a desire to give expression to 

 my views upon botanical nomenclature. Under the circum- 

 stances, I must speak briefly and somewhat dogmatically. In 

 my opinion botany is the science of plants and not the science 

 of names. Nomenclature is only one of those tools which is 

 necessary to botany, and this being the case, points of nomen- 

 clature should be subordinated to science, 



A principle of botanical convenience has been established 

 by those who prefer one name to another on account of ex- 

 pediency or convenience. This principle should have a great 

 deal of influence. It has been so recognize! by the greatest 

 botanists, and from their authority receives great weight. I pre- 

 fer the word expediency as a better term than convenience to 

 designate the principle, that the demands of science over -ride 

 any merely technical claims of priority, &c. 



Priority of specific names appears to be based entirely upon 

 one section of the code of 1867. That simply says that 

 when a species is transferred from one genus to another, the 

 specific name is maintained. This principle is usually under- 

 stood and applied in the way that the oldest specific name 

 has a right in all cases to be retained. It cannot fairly be so 

 interpreted and applied, since it governs only to the extent 

 that this should be the law, but it is not to be made an ex 

 post facto law. Thus when a transfer has been made, that 

 ends the matter so far as the choice of a specific name is con- 

 cerned, and no one is authorized to take up a different name. 

 This practice of retaining the oldest name under the genus, 

 no matter what older specific names there may be, was 

 adopted by Dr. Gray in his later years and by the Kew bot- 

 anists, for the reason that once established and pretty generally 

 recognized, it would avoid the great mass of synonymy, which 

 is being heaped like an incubus upon the science. I must 

 express surprise that Dr. Britton had not considered it his duty 

 to publish the last written words of Dr. Gray which were 

 addressed to him upon this subject and which expressed his 

 positive opinions upon this point. 



There is nothing whatever of an ethical character inherent 

 in a name through any priority of publication or position 

 which should render it morally obligatory upon any one to 

 accept one name rather than another ; otherwise it would be 

 applicable or true as well in the case of ordinal names, mor- 

 phological names, teratological, and every other form of 

 name, to which now no one feels himself bound to apply the 

 law of priority. The application of this law as at present 

 practised by many botanists, which would make it the one 

 great law of botanical nomenclature, before which every other 



^ From Botanical Gazette, vol. xvii. 



NO. I 103, VOL. 47] 



must yield regardless even of common sense, is a mere form 

 of fetichism exemplified in science. Many instances of the 

 application of this law aie not science but are rather supersti- 

 tion. Sereno Watson. 

 February 22, 1892. 



The Reflector with the Projection Microscope. 



The lantern is now u«ed for so many purposes — scientific, 

 photographic, and recreative — that any improvement in its 

 construction will be acceptable. When we look into this 

 instrument whilst at work we must be disappointed at the large 

 quantity of light lost by reflection and by dispersion — light 

 which ought to go to the illumination of the screen. In the 

 ordinary form of the lantern three lenses of dense glass are 

 employed as condensers. Each of these six surfaces reflects 

 and scatters the light, and the glass itself is absorbent of its 

 rays. 



The dioptric construction of the projection lantern has been 

 well worked out by Messrs. Wright, Newton, Salomons, and 

 others, but the catoptric principle, which would eliminate 

 almost entirely these disadvantages, has been scarcely at all 

 studied. 



Although my experiments have been made solely with the 

 limelight in various forms, the following remarks may equally 

 apply to light given by the electric arc : — 



If a reflector be used instead of the ordinary condensers it 

 is obvious that the position of the lime cylinder must be reversed. 

 This will present no difficulty, for the tube holding the jet can 

 be bent into a helical form. The dark image of the lime- 

 cylinder also will have no more practical disadvantage than is 

 experienced by a like image formed by the small plane specu- 

 lum of the Newtonian telescope. 



As to the mirror itself, although a parabolic form is the most 

 correct, a spherical surface will be sufficient for mere illumin- 

 ating purposes, and thus expense may be spared in the grind- 

 ing of the more difficult curve. A speculum of from 5 to 7 inches 

 diameter, having a radial curvation of from 2^ to 3 inches, 

 will grasp a large quantity of light, much more than that ob- 

 tainable from the 5-inch condenser usually employed. 



Silver deposited by one of the various reducing processes on 

 the surface of a clear glass lens will have many advantages over 

 a metal mirror. The front surface will give perhaps the finest 

 definition, but by silvering the back part of a spherical glass 

 film, or that of a ground lens, the brilliant surface will remain 

 untarnished for an indefinite time, and the whitish bloom 

 formed by slow volatilization of the incandescent lime is easily 

 removed. This silver film adheres with remarkable tenacity, 

 and it will bear a great deal of heat without blistering or 

 becoming detached. 



I have had considerable success in constructing such mirrors 

 from the large ornamental glass spheres blown in Germany, and 

 silvered within by Liebig's process, viz. with milk sugar and 

 ammonio nitrate of silver. A glass sphere of 10 or 11 inches 

 in diameter may be easily cut into eight or nine mirrors by a 

 red-hot iron, and this without disturbing the silvering, which 

 will require only gentle friction with a pad of cotton impreg- 

 nated with a trifle of rouge to brighten it. Thus, at the cost of 

 a few shillings, eight or more mirrors can be made, and also 

 provision be made against possible accidents of cracking by 

 heat. 



The light-radiant is so placed that the secondary focus is inter- 

 cepted by a plano-concave lens of dense glass, as has been hap- 

 pily proposed by Mr. L. Wright. The convergent rays from the 

 speculum are thus made into a parallel beam, which must be de- 

 prived of its heat by an alum-trough, for the light and heat at 

 the substage condenser is very great. 



Convergence, I find, is usefully promoted by a plano-convex 

 lens of about eight inches focus, placed two or three inches 

 before the above-noted plano-concave lens. In all other respects 

 the arrangements are like those of the usual modern projection 

 microscope. 



I have pretty constantly used the ether-oxygen saturator, and 

 I consider it to be perfectly safe, if ordinary precautions be 

 taken. The oxygen, compressed in cylinders, is much recom- 

 mended, as there can be no mixture of vapour, except at the 

 right place. The U-shaped horizontal saturator, plugged with 

 flannel, must be well charged with ether, or with the best gaso- 

 lene, and care should be taken, before beginning or ending an 

 exhibition, to shut off the oxygen tap before closing the ether 



