.154 



NATURE 



[April 19,1917 



that the atmosphere of London is far from being an 

 astronomer's ideal, all the observations which led to 

 the discoveries on which his fame rests were made 

 in London. This great Cathedral seems the appropriate 

 resting-place of a memorial to one whose life and 

 work were so linked up with this city. 



Sir William Hugefins was a prominent example of 

 a type of man to whom English science owes much, 

 the' non-olficial worker. Like his contemporaries, 

 Darwin and Joule, he never held any professorship 

 or scientific appointment. When in 1858 he retired 

 from business at an unusually early age, he seems 

 to have been undecided as to whether he should 

 devote himself to the microscxjpe or the telescope. The 

 telescope gained the day, and he built an observatory 

 at Tulse Hill; he began by making drawings of the 

 planets, but seemed to be losing interest and to be 

 rather despondent, when Kirchhoff's determination of 

 the chemical elements in the sun by the aid of spec- 

 trum analvsis came to his knowledge. This was to 

 him, he said, like water in a thirsty land, and he 

 determined to attempt to find out the constitution of 

 the stars by the same method. At the beginning of 

 1862 he persuaded Prof. Miller to join with him in 

 the work, and in spite of the formidable difficulties 

 due to the feebleness of the light, the mechanical diffi- 

 culties of keeping the image of the star on the slit 

 of the spectroscope, and the caprice of the London 

 atmosphere, they were able to present to the Royal 

 Society in 1863 a preliminary statement as to the 

 spectra of some of the brighter stars, while in 1864 

 they published in the Philosophical Transactions of 

 the Royal Society a general account of the spectra 

 of about fifty stars, with a detailed study of some of 

 the more important ones. They showed that the stars 

 are made up of elements which, with few exceptions, 

 are found in the earth. In 1864 Huggins made a 

 discovery of capital importance in connection with 

 the evolution of the stars, for he discovered a nebula 

 the spectrum of which showed that it consisted of 

 glowing gas, and was therefore in quite a different 

 state of development from the stars he had examined, 

 the spectra of which showed that their physical con- 

 dition was analogous to that of the sun. Huggins 

 threw himself with characteristic energy into the study 

 of the spectra of the nebulae, and found that the 

 nebula were not all of one kind; some were stellar 

 aggregates, while others were continuous masses of 

 incandescent gases. 



The importance of these results and the interest 

 they excited were recognised by scientific societies 

 with a promptitude almost -without parallel. Three 

 years after beginning serious scientific work he was 

 elected a fellow of the Royal Society, the next year 

 he was awarded a Royal medal, and after ten years 

 he seems to have been elected to almost every scientific 

 society in Europe. The work which commenced _with 

 such brilliance was carried on with undiminished 

 ardour for nearly fifty years ; since 1875 with the active 

 co-operation of "his wife. It showed throughout the 

 characteristics so noticeable in the earlier work : the 

 power to select the right problem to attack, the ability 

 to devise the best way to attack it, and the industry 

 to take boundless pains in overcoming the difficulties 

 which sprang up at every turn. 



On behalf of the Royal Society, I record with grati- 

 tude the help he -gave to the work of that society, 

 and especially to the distinction and dignity with 

 which he for five years discharged the office of presi- 

 dent. For the medallion we are indebted especially 

 to Mr. Pegram, the artist whose skill has produced it, 

 and to Miss Montefiore, who has borne the burden 

 of the heavy work necessary to bring such a scheme 

 to completion. 



NO. 2477, VOL. 99] 



THE DEVELOPMENT OF VEGETATIONA 



CONSIDER-ABLE scepticism is not infrequently ex- 

 pressed by botanists who are not ecologists as 

 \o the possibility of formulating a satisfactory natural 

 classification of vegetation, i.e. of plant comuuinities ; 

 and this scepticism is natural enough when we con- 

 sider the numerous attempts, largely inconsistent and 

 contradictory, that have been made in this direction, 

 especially irl recent years. It is obvious that the ulti- 

 mate test of validity will be general acceptance, and 

 certainly we cannot claim that there is anything like 

 agreement among ecologists as to a natural scheme or 

 as to the principles upon which such a scheme should 

 be based. At the same time, it must be remembered , 

 that it took a very long time and constant efforts from ■ 

 many quarters to arrive at a natural system of classi- 

 fication of species which commanded anything like 

 general acceptance. The task of the classifier of plant 

 communities is much more "difficult for many reasons, 

 the chief of which is that the outlines of the classifi- 

 catory units — the plant communities— are frequently 

 vague and shifting, owing to the multiplicity of causes 

 and combinations of causes which determine their 

 nature and limits. Some would doubtless go so far 

 as to say that the units themselves are illusory,, but 

 it is significant that this is not the view of those who 

 have seriouslv studied vegetation in the field. 



The natural system of species has been ultimately . 

 established on a phylogenefic— i.e. a developmental- 

 basis, and any other was impossible once the principle 

 of evolution had been accepted. Prof. Clements's 

 fundamental contention in the volume under review is 

 that the natural system of plant communities must 

 also be established on a developmental basis, and he 

 includes in his purview not only present vegetation, 

 but all the past vegetations that have come into exist- 

 ence since plant-life first appeared on the earth. .\s 

 the basis of this contention Prof. Clements claims that 

 the plant formation — his basic unit — is an organism. 

 Whether that claim can be admitted or not depends, 

 of course, upon our conception of an organism. Start- 

 ing with individual animals and plants, which are the 

 typical, or, as some might say, the only, organisms, 

 it is clear that we can, if we so choose, extend the con- 

 ception to human societies, for instance, which certainly 

 have very many of the same characteristics, though 

 they have not the close-knit spatial unity of structure 

 and function of the individual plant or animal. If we 

 extend the conception further to include plant forma- 

 tions in Clements's sense, we drop from our concept 

 one of the characteristics of the higher animal organisms 

 and of human communities — the conscious co-operation 

 of parts in pursuit of the ends of the whole. ^ But 

 neither is this a character found in the lower animals 

 or in plants. Unless, therefore, we definitely restrict 

 our conception of organism to individual anirnals and 

 plants, we must concede Clements's contention that 

 plant formations are organisms, and if we do so 

 restrict it we have perforce to admit that the plant 

 formation has many of the characters of organisms, 

 a fact which we may perhaps express by calling the 

 vegetation unit a quasi-organism. 



Prof. Clements's plant formation is the plant com- 

 munity in equilibrium with its climatic habitat, i.e. 

 deterrnined and kept constant by the control of a dis- 

 tinct climate. The type of such a formation is the 

 forest of definite floristic composition which maintains 

 itself indefinitely so long as the climate maintains its 

 general character. Prof. Clements points out _ that 

 such a community has a definite organisation, i.e. a 

 fixed spatial and functional relation between the plants 



1 "Plant Succession: an Analysis of the Development of Vegetation." 

 By Prof. F. E. Clements. Pp. xiii + 5124-61 photographic plates and 51 

 figures in the text. (Carnegie Institution of Washington, 1916.) 



