April 19, 19 17] 



NATURE 



155 



composing it and with the substratunn : it regenerates 

 destroyed parts, and can reproduce itself in new situa- 

 tions ; and, finally, it has a definite development or 

 ontogeny. 



It is this last feature with which the present volume 

 is concerned. On bare ground or in water, within the 

 climatic limits which determine the particular forest 

 formation, there develops a succession of plant com- 

 munities which ultimately gives rise to the forest. The 

 causes of succession are the reactions of the successive 

 plant populations on the habitat, which render it favour- 

 able to particular new invaders and less favourable to 

 the existing occupants. The final stage, or climax, is 

 reached when equilibrium is established and invasion 

 no longer possible. The earlier course of de- 

 velopment differs according to the nature of 

 the substratum on which succession occurs, 

 but the later phases correspond whatever the 

 origin of the succession. This has been amply estab- 

 lished in the case of several of the great forest climax 

 formations of North America. As a particular instance 

 W. S. Cooper has worked out in strikingly complete 

 detail the successions culminating in the climax forest 

 of Ahies balsamea, Betida alba, var. papyrifera, and 

 Picea canadensis on Isle Royale, Lake Superior. The 

 primary successions in this case start from the bare 

 rock shore or beach (xerarch successions), or from 

 bogs and delta swamps (hydrarch successions), and 

 through distinct series of definite and constant plant 

 communities converge to the climax forest. Secondary 

 successions are initiated by forest burns. If the 

 humus is burned the resulting secondary succession 

 is like the beach succession. When the humus is not 

 burned the regeneration of the climax forest is much 

 shorter. 



In regions the climate of which does not permit of 

 the establishment of forest the climax formations are 

 of other vegetation types, such as desert or grassland ; 

 and here the successions from bare soil oi water to the 

 climax are shorter because woody plants are not 

 involved. 



Prof. Clements recognises the existence within the 

 formation of associations which are " climax communi- 

 ties associated regionally to constitute the formation," 

 and "are recognised chiefly by floristic differences." 

 He thus maintains the practice almost universally 

 agreed upon among ecologists of making the associa- 

 tion a subordinate unit to "the formation. Successively 

 subordinate units of the association are designated as 

 consociation (dominance of a single species), society, 

 and clan. Parallel units are distinguished in the 

 development series — i.e. those leading up to the forma- 

 tion in succession. 



The author's foible is undoubtedly the multiplication 

 of terms, a great number of which are proposed in 

 this memoir. This is the concomitant of the compelling 

 necessity he feels to establish complete systems of con- 

 cepts logically worked out in ever\- detail. Without 

 entering upon a criticism of the validity, of the con- 

 ceptual systems themselves, which would occupy far 

 more space than is at our disposal, it may be pointed 

 out that the normal human mind invariably refuses to 

 accept new concepts and terms until the progress of 

 our knowledge of the relations of phenomena compels 

 their adoption. It can scarcely be said that all 

 ,Prof. Clements's terms are essential to clearness of 

 thought and description. Some of them will no doubt 

 come into general use, as some of the terms proposed 

 in the author's "Research Methods in Ecology" (1905) 

 have done. 



The present work shows a great advance in 

 maturity as the result of a wider experience, and 

 is notable as the first systematic account of a funda- 

 mental phenomenon in vegetation. Its outstanding 

 merit is logical thoroughness and completeness. It is 

 NO. 2477, VOL. 99] 



impossible even to indicate the ground covered within 

 the space of a short article. 



The numerous photographs deserve- quite Special 

 praise. They are not only of uniformly high standard 

 and excellently reproduced, but they are admirably 

 chosen to illustrate the text. A. G. T. 



THE ZOOLOGY OF THE "TERRA NOVA'' 

 EXPEDITION. 



"ppOUR further reports on the zoological material 

 ■*• collected during the British Antarctic {Terra 

 Nova) Expedition, 1910, have recently been issued by 

 the British Museum (Natural History). Miss Massy 

 {Zool., vol. ii.. No. 7, pp. 141-1.76, 43 figs.) describes 

 sixty-eight specimens of Cephalopoda, which belong 

 to seventeen sf)ecies and twelve genera. Forty of the 

 specimens belong to the Octopoda, the abundance of 

 the genus Moschites being noteworthy. . 



The Decapod Crustacea, described by Mr. Borra- 

 daile (vol. iii.. No. 2, pp. 75-110, 16 figs.), comprise 

 fort>'-six species, but only three of these — all t£iken 

 in the Ross Sea — are antarctic. In his account of 

 Crangon antarcticus, Mr. Borradaile points out that 

 the aflftnities of this antarctic shrimp lend some sup- 

 port to the hypothesis of bipolarity. One of the most 

 interesting of the Decajxxls, a species of Porcellano- 

 pagurus taken off the northern end of New Zealand, 

 forms the subject of a separate report (No. 3, 

 pp. 111-126, 13 figs.). Mr. Borradaile points out that 

 Porcellanopagurus is one of the many attempts of 

 Nature to evolve a crab. This crab seems to have 

 been evolved from an ordinary hermit-crab, and the 

 method followed was not only, as, in other such cases, 

 a broadening and depressing of the cephalothorax 

 together with a reduction of the abdomen, but 

 also a drawing out horizontally of the edges of 

 the hard plate which roofs the fore part of the 

 body of a hermit-crab. Mr. Borradaile traces 

 the relations between the various external features 

 of Porcellanopagurus and those of a hermit- 

 crab. He surveys other routes by which evolu- 

 tion in the direction of " carcinisation " has pro- 

 ceeded throughout the Anomura, and reaches the 

 conclusion that there is in the constitution of the 

 Anomura a disposition or tendency to achieve that 

 special formation of body which constitutes a crab. 

 Whether the tendency be primarily one of morphology 

 or of habits is another question, but, seeing that a 

 similar form of body has been reached independently 

 in circumstances which must have needed very dif- 

 ferent changes in the habits of the animals, it would 

 appear that a morphogenetic tendency is the primary 

 factor, but that it can only be realised in the event 

 of the development of suitable habits. Mr. Borra- 

 daile remarks that there are few better instances 

 than those afforded by "carcinisation " of the fact 

 that the organism is, after all, the dominant factor 

 in evolution. 



In No. 4 (pp. 127-136, 7 figs.) Mr. Borradaile gives 

 an account of the fourteen species of barnacles 

 brought back by the expedition. The most interest- 

 ing specimens described are some valves, referred to 

 a new species of Hexelasma, collected in a glacier, 

 30 ft. above sea-level, in Evans Cove, Teira Nova 

 Bay. It is -not possible to state from their appearance 

 whether these valves are recent or fossil, but it seems 

 scarcelv probable that they are recent, for no trace 

 of such a barnacle has been found in any collection 

 from either the Ross Sea or elsewhere, nor can any 

 satisfactory suggestion be made as to the wav in 

 which recent shells could have reached the position 

 in which these were found." If they be fossil, it 

 seems highly probable that they are, if not of Miocene 

 age (their nearest known relation is H. aucklandicum 



