494 



NATURE 



{April 1 8, 1872 



tion were immersed, the copper in a pure, /.(•. deoxygenised, 

 solution of nitrate of copper, the silver in an oxygeniscd solu- 

 tion ; the two liquids communicated through the diaphragm of 

 a divided cell. In half an hour the silver plate was covered with 

 a reddish film, while not a trace of oxidation was perceptible on 

 the copper. On continuing this experiment for three hours, it 

 was found that the copper plate lost O'oojgnn., and the silver 

 plate increased proportionately. On cleaning the plates and re- 

 versing their position, the copper was covered with a film of 

 oxide, while the silver remamed free from cupreous deposit. 

 We believe, therefore, that tlirough the simultaneous action of 

 the two metals the dissolved salt is put into such a state of ten- 

 sion that oxygen brings about a chemical change which other- 

 wise would be impossible, and that this change is initiated in 

 close proximity to the more negative metal. 



Though we have examined only this reaction, we have satisfied 

 ourselves that it is not an isolated fact. Each of the elements 

 concerned may be replaced by others : thus the sulphate may be 

 substituted for the nitrate of copper, or platinum may be used 

 instead of silver. Chlorine may take the place of oxygen with 

 the production of the subchloride instead of the suboxide, and 

 zinc may be employed as the positive metal with zinc chloride as 

 the salt in solution, in which case copper may be taken as the 

 negative metal, and on its surface wiU form a deposit of oxide of 

 zinc. 



Linnean Society, March 21 and April 4.— Mr. Bentham re.id 

 the continuation and conclusion of his no'es on Composite', 

 comprising their History and Geographical Distnbution. The 

 ancient history of the order is more purely conjectural than that 

 of many other large groups of plants. The geological record is 

 remarkably scanty. The only remains that can be plausibly 

 referred to Conjposita" are the impressions of achenes with their 

 pappus figured by Oswald Heer from the upper Miocene deposits 

 of central Europe, which, supposing, as is probably the case, that 

 the identifications are correct, would only show that at that ter- 

 tiary epoch Composita: existed in Europe of the same general 

 character as those which are there now to be met with ; and that 

 they had thus already attained that highly ditiferentiated charac- 

 ter they now possess, and consequently must already have been 

 of an old date. In the absence, therefore, of direct evidence, 

 we are left to judg;; of the antiquity and orighi of Composila; in 

 general, as well as of the subordinate races they comprise, from 

 their comparative structure and geographical distribution. The 

 paper then proceeds to pass in review in great detail the thirteen 

 tribes of Composite, and the several subtribes and principal 

 genera into which they are divided ; after which some conjec- 

 tures are put forward, as derived from the data thus supplied, 

 as to the comparative antiquity of the principal races of Com- 

 posita;. Concurring with the arguments which have been 

 brought forward by French and other botanists, to show that the 

 great consolidation and uniform structure of the essential organs 

 of fractification in Composita; are evidences of their greatest 

 perfection and consequent comparatively recent origin, it is 

 shown that this consolidation and uniformity is least marked 

 in Helianthoidea:, especially in the small subtribe of Petrobiere, 

 and most so in Cichoracea> ; and this conjecture that the 

 former represent the most ancient, the latter the most recent, 

 races of the order, is confirmed in some measure by the pecu- 

 liarities of their respective geographical distribution. The 

 study of the various details given would further lead to the sup- 

 position that the primitive form of Composite had regular 

 gamopetalous flowers with an inferior ovary, the calyx, corolla and 

 uniseriate stamens isomerous and probably pentamerous, the pistil 

 bicarpellary, but the ovary already internally reduced to a single 

 cell with a single erect anatropous ovule, and the seed exalbu- 

 minous, enclosed in an indehiscent pericarp, and containing a 

 straight embryo with an inferior radicle ; and that it is in the 

 gradual course of subsequent consolidations that the bracts have 

 crowded round the condensed flowers and usurped the functions 

 of the calyx-limb, which has become obliterated or transformed 

 so as to be better adapted to its new duties ; the corollas have 

 become contracted, or the outer ones variously developed in 

 forms and colours adapted to assist in the process of cross- 

 fertilisation ; the anthers, brought into close contact by the com- 

 pression of the flowers, have become united, and their styles 

 modified so as to assist them in the discharge of their pollen, 

 and the conversion from hermaphroditism to unisexuality may 

 in various races have variously preceded or followed some or all 

 of these changes, and produced those numerous diversities 



observed in the order. We might be further led to imagine that . 

 several of these changes had taken place at a very early period 

 previously to the disruption of or stoppage of communication 

 between the tropical regions of the globe, that, besides the ^ 

 ]iarent forms above supposed to be represented in some Helian- 

 thoidea:, and perhaps a few Cotulefe, Composite then existed, 

 showing several important modifications, such as— (i) the regu- 

 lar and uniform tubular development of the corolla, accompanied 

 by more or less of suppression of the inner bracts, and of the 

 normal calyx-limb, with a substitution of a pappus in the latter 

 case ; (2) the reduction of the corolla limb, attended fre- 

 quently by a sexual dimorphism and occasional oblique 

 development of the outer female flower ; and (3) perhaps at a 

 later period, the uniform unilateral development of the whole of ?j 

 the corollas, accompanied usually by a suppression of the inner i^ 

 bracts and conversion of the calyx limb into a pappus. From 

 the first of these modifications would have sprung the Eupato- \ 

 riacex in America, the Vemoniacea; in the New and the Old ' 

 World, the Cymroides in the northern, and the Mutisiacere in 

 the southern hemisphere. From the second modification would 

 have arisen— first, the more slightly altered Helianthoide.-c chiefly 

 in America ; secondly, the Helenioidece in America, and the ^ 

 Anthemidea: in the Old Worid, with the thinly paleaceous 

 inodification or total suppression of the inner bracts and calyx : 

 limb ; and thirdly, the cosmopolitan Senecionide.-e, Asteroidea;, .' 

 and the majority of Inuloide.x', with an almost universal suppres- ' 

 sion of the inner bracts and conversion of the calyx limb into a 

 setose pappus. The third general modification, with a very few 

 slight exceptions, has settled down into those Cichoracea; whose ^ 

 absolute uniformity had been already pointed out. In the third 

 and concluding portion of the paper the present Regions, or chief 

 centres, or areas, of the principal races of Composita: are passed 

 in review. The position of these great centres is evidently ' 

 influenced by the prevalent constitution of the order, and the e 

 consequent effects of climatological and other physical causes on ' 

 the gradual migrations of its species. Rarely arborescent and 

 gregarious, still more rarely aquatic, Composita; are, in a great '■- 

 measure, excluded from the vast forest-clad lowlands of the ' 

 Amazon region of America, or of eastern tropical Asia, and the > 

 species are few in the swampy bogs of the northern hemisphere. 

 Their favourite haunts are treeless or thinly-clad mountain 

 regions, and especially the lower or broken grounds, rocky ridges, ' 

 or open camposof warmextratropicalorsubtropical districts. They 

 may be met with, it is true, at the highest altitudes or latitudes 

 which will bear phtcnogamic vegetation as well as in the warmest ' 

 tropical deserts, and a few species, as ready colonists, are per- 

 fectly ubiquitous in the traces of man ; but there are large 

 tracts of open countryespeciallyaboundingin highly differentiated ■ 

 races of very limited areas, others again where Composite genera 

 and species are as numerous and ill-defined in their subordinate 

 races as wide and vague in their geographical range. These ' 

 tracts of country severally constitute the centres of differentiation 

 or areas of preservation, of which the definition is attempted as 

 Regions of Composita;. After alluding to the difficulties arising ' 

 from the interchange of races across the frontiers of adjoining ' 

 regions, or from the occasional reappearance of identical genera 

 and species at enormous distances, as well as from our imperfect ■ 

 acquaintance v^ith the Composit.ie of certain districts, these • 

 regions are severally passed in review, in a series of tables of the 

 genera they contain, either endemic or common to other regions, 

 followed by such general observations as the comparisons may 

 have suggested, commencing with the primary division into the ' 

 New and the Old World, the former including the Sandwich as 

 well as the more nearly placed Pacific Islands, whi'st the A tlantic ' 

 islands, Australia and New Zealand, are compris d in tl e Old ■ 

 Worid. After a general table of the genera of and estimated 

 number of species in each division, a series of tables shows — (1 ) the 

 connections between the tropical regions of the t\vo divisions, as 

 exemplified by identical genera ; (2) the same connections' in 

 identical species; (3) the northern, and (4) the southern connections 

 of the New and Old Worlds. Generally Composite are nearly ' 

 equally divided between the two, about 430 genera in the New 

 and 410 in the Old, with at least 4,700 species in the former, 

 4,400 in the latter ; new discoveries being likely to add more to 

 the latter. Of these numbers about 75 genera are common to 

 the two divisions, but the identical species are under 70 out of 

 at least 9,100. These common species are chiefly Arctic, or 

 high northern, the tropical ones being very few and mostly very 

 generally diffused, and ready colonists, such as Edipta alba, 

 Ageratui}uonyzoiJes,Adcnostemmaviscosii?n,SicgesbeckiaoriatiaHs. 



