January, 1953 REVIEWS 233 creased the usefulness of his book by listing and the principles and laws will be tested by them for reference and citing them in the proper comparison, discussion and new investigations. place in the text. PIERRE DANSEREAU As it stands, the book is certain to offer much DEPARTMENT OF , stimulation to further research and exploration. UNIVERSITY OF MICHIGAN, The descriptions will be developed by local study ANN ARBOR, MICHIGAN

INTEGRATION OF THE EcoSPECIES 1 The etetnally disputed definition of species is very mechanisms observed are sure to be quite very sharply focused in Jens Clausen's book, different in other parts of the world with broad "Stages in the of plant species." The instead of narrow life zones. Stebbins for in• outstanding merit of this work is that it sum• stance (Am. Nat., 86 (826) : 34, 1952) ventures marizes very lucidly the experiments on the na• to "predict that the diversity of ecotypes of ture of species which Hall had begun but which individual species, when investigated will prove are principally Clausen's own work and that to be considerably less" in the Eastern States of his collaborators David D. Keck and Wm. M. than in . Hiesey at the Carnegie Institution of Washing• The book consists of eight chapters. The first ton's Department of Plant Biology in Stanford, two offer a brief historical perspective in which California. The past decade has been a very the growing influence of on fruitful one for this group, as the essentials is emphasized. The principal currents are out• and much of the detail of their experimental lined: Darwin's keen observations of variation work have been made known in print. The in nature and its obedience to natural selection; soundness of their method, the thoroughness of the experimental approach and discovery of the their investigations and the variety of their mechanics of heredity by Mendel's successors. respective backgrounds offered unique guaran• These two traditions, which to some extent had tees of original and significant research. Their followed separate courses, are joined harmoni• three book-length memoirs and their many ously in Turesson's work. The often over• shorter papers had provided us with a great looked evolutionary ideas of Linnaeus in his later wealth of new materials and many leads to new years are quoted as marking the beginning of a interpretations. The present book goes a step "modern" point of view. Jordan is credited beyond this and outlines Clausen's (and pre• with the discovery of the local population. sumably his collaborators') emergent concept This is the subject of the third chapter, "The of speciation. This is far-reaching indeed, al• local population as the basic evolutionary unit." though the author does not pretend to review Here the author's working principles are clearly the whole field of experimental taxonomy, even stated: "It is at the level of the local popula• less the more general topic of evolution. In tion that all of the selective forces act upon fact, it justifies its title perfectly by casting the genetic resources of the population." This complete emphasis on experimentally known statement is well illustrated and substantiated cases of perfect to imperfect to inadequate iso• by examples from the genera Layia, Viola, lation of taxa in the Western North American Potentilla, and Achillea. Following the best in environment. Some of the author's earlier work taxonomic tradition, intra-population and inter• in Northwestern Europe is also quoted, as are population variations are compared and found Brainerd and Gershoy's in Eastern North to be of a different order of magnitude (p. 26). America. But no one will quarrel with Clau• However, these analyses are always made in sen's dwelling principally on what he knows the light of the deeper-lying physiological re• best : a central Californian transect from the sponses which are elicited by the heredity vs. Pacific across the coastal ranges and inner val• environment contest. Thus: "It is probable leys to the slopes and summits of the Sierra that the intrapopulation variation enables a spe• Nevada, thence down to the deserts of the Great cies to tolerate periodic variations in the cli• Basin. Such a transect lends itself extremely mate at any one locality." well to a test of evolutionary processes as it These various points are strikingly illustrated provides strongly contrasting environmental by experimental data, the conclusiveness of which backgrounds at close intervals. Even though is quite incontestable. One might wish, how• such telescoping is not unique, it is in many ever, that Clausen's rejection of other tech• ways peculiar and the rates of change and the niques for estimating populations "growing in the wild and therefore subjected to uncontrolled 1 Clausen, Jens. 1951. Stages in the evolu• modifications in many environments" were the tion of plant species. viii + 206 pp., 76 figs., object of further discussion. The work of Ed• Ithaca: Press, $3.75. gar Anderson, Fassett, and Woodson is not men- 234 REVIEWS , Vol. 34, No. 1 tioned. It would be interesting to compare pur• Thus some local populations of both subspecies pose and achievement in both cases and to out• share the same amounts of rainfall and heat line what aspects of environmental integration except inasmuch as their habitats ("sunny slope" are revealed by these different means. It seems, and "meadow") utilize the meteorological ele• however, that both groups will agree that ments differently and eventually provide the "clines are not commensurable with natural en• plants themselves with rather different amounts tities," if by the latter are meant formal taxa. of heat and water, and at different times also. The fourth chapter concerns "the evolution of There is here an ecological dimension that fits ecological races." Whereas the preceding chap• into a climatic dimension. There is also the ter had not provided a hard and fast definition further question of ecological amplitude, not of the local population, the present definition of necessarily similar or even parallel to climatic the ecological race may seem unsatisfactory: tolerance. 2 Although these issues are certainly "An ecological race is usually composed of a present in the author's mind, they are not as considerable number of variable local populations sharply focused as the corresponding morpho• existing within a given ecological zone." This logical and genetic aspects. latter term itself is not defined either, except by In the fifth chapter the genetic systems which implication. A short paragraph on parts of underlie the adjustment of taxa are reviewed, pp. 50-52 states that "these major sets of fac• whether or not the units involved show any tors in the environment have been decisive in morphological discreteness. The point is well the development of ecological races, namely, made that some formerly adaptive features are climate, soils, and other organisms. All of able to persist after a shift and even a reversal these three are interrelated and contribute to in the .kind of environmental pressure exerted. natural selection, but climatic, edaphic, or biotic Thus a "typically maritime" Viola tricolor (from ecotypes can be recognized, depending upon ) was grown in inland California and which of these sets of factors has been rela• eventually sowed itself in a garden at Santa tively the most dominant." Rosa, maintaining its identity under "drastic I can voice no objection to the above state• changes." s ments but I am afraid they lend themselves to Several good examples are provided here that a variety of rather divergent applications. illustrate the degrees of effectiveness in genetic Whereas a constant attempt is being made to isolation. It is assumed that the best proof assess morphological, genetic, cytological and thereof lies in the failure to cross-breed or in physiological criteria and to assemble them in the relative weakness of the offspring. Thus a discriminating way so as to reflect a natural the background is drawn for the principal argu• hierarchy (Chapter VIII), and whereas the ment of the book which will culminate in a magnitude of each "stage in the evolution of grading (Chapter VIII) of the isolating mecha• plant species" is graded, no corresponding nisms. The largest stock of evidence along hierarchy in the environment as a whole is in• these lines is drawn from taxa indigenous to at dicated. Transgressions by the segments of a least one of the three stations (Stanford, species beyond the barriers of biotope, com• Mather, Timberline) operated by Clausen and munity, habitat, climatic zone are not recog• his collaborators. The relative frequency of nized explicitly as such. successful experimental crossing on the one Clausen does not say that hierarchy in en• hand, and the degree of survival and "vigour" vironment (a) does not exist ; ( b) is too com• plex to be measured effectively; ( c) is not sig• 2 A plant like Chamaedaphne calyculata ranges nificant, since the ultimate unit alone is con• from the near-Arctic to the mountains of sidered. For instance, Figure 5 (p. 20) shows Georgia, is exposed to a variety of severe and 4 subspecies of Potentilla glandulosa as they oc• mild climates. Ecologically it is very narrow, cur from 900 to 11,000 feet on the west slope however, being strictly confined to bogs, and of the Sierra Nevada. As far as major climatic even to a certain phase of bog formation. On and vegetation zones· are concerned, 6 distinct the contrary, Betula populifolia has rather a units are involved: 1) the oak savana, 2) the yel• narrow range (Atlantic-North Appalachian) low pine forest (or woodland), 3) the red fir but very wide ecological amplitude : sand plains, forest, 4) the lodgepole pine woodland, 5) the bogs, old fields, stream edges, rock outcrops, white-bark pine scrub and 6) the alpine meadow. etc. Ssp. typica is found only in 1; ssp. reflexa in 1 s A similar case is that of Veronica peregrina and 2 ; ssp. hanseni in 2 and 3 ; ssp. nevadensis var. laurentiana, an estuarine ecospecies now self• in 4, 5, and 6. The case of reflexa and hanseni sown in the Montreal Botanical Garden where is an interesting one as they overlap to a con~ it maintains its identity perfectly. (M. Ray• siderable extent geographically (and therefore mond and J. Kucyniak in Contrib. Inst. Bot. climatically), but remain distinct ecologically. Univ. Montreal, 62: 19. 1947). Jan.uary, 1953 REVIEWS 235

in each one of the three stations on the other ecosPecies are necessary terms at this time, al• hand, show both the amount of divergence be• though taxonomists are justly reluctant to speak tween related taxa and the amount of relative in terms of "morphological species" and "genetic fitness· of each to its station, although not as ob• species" (terms which are generally avoided in viously to its hahitat(s), even less to its com• this book. Rather they are willing to test this munity ( ies). and that taxon by the use of new criteria (genetic, Chapter VI outlines "the evolution of inter• ecological, and otherwise) and to redefine and specific barriers," starting with a "situation recast them nearer to experimentally known within species where such barriers have not reality without deviating from the classic no• yet started to evolve," or at least where they menclature. This however is essentially a "le• are not effective because of gene flow through gal" point of obviously little biological interest. intermediate segments. It remains that the experimental taxonomist, Although "there are numerous ways in which when he deals in ecospecies, cenospecies, etc., groups of populations and races may become has a more unequivocal term than the taxono• genetically isolated . . . the most normal pat• mist whose categories are for the most part un• tern of speciation ... is a more or less simul• tested. taneous and gradual separation in morphologic, Clausen's hook is an exceedingly important one ecologic, genetic, and cytologic characteristics." to ecologists. If their research is concerned Clausen then goes on to review "groups having with autecological relationships, they can make predominantly ecological barriers," "predomi• no beginning unless they constantly bear in nantly morphological differentiation,'' "predomi• mind the phenomena which are so capably out• nantly genetic barriers." These three different lined here, unless they are at all times aware kinds of taxa are amply illustrated by Californian of the underlying mechanisms of variability in examples, each type showing well-defined char• local populations and ecological races and be• acteristics both in morphology and behaviour. come able to detect them. Although this little As weak barriers tend to become strong, so hook does not cover all phases of the integration scarcely separable units separate further, and of plants in their environment-which is in• better individualized taxonomic units result. deed not its purpose--it so sharply focuses the In Chapter VII, the author applies the foregoing genetic substratum of adaptation that it pro• principles and further synthesizes the wealth of vides a useful background for practically all facts at his command to describe "the evolu• cases. tion of groups of species." The genera Layia, If the ecologist's. research concerns synecology, Madia, and H emizonia in California show very he will find much that is lacking in this book. distinct patterns which are essentially the re• He will regret that synecological concepts are sult of different degrees of divergence at all nowhere as clear levels, from the local population to the genus. as are genetic and taxonomic The violets, on the other hand, offer a more concepts. He may feel that much has been said complex situation, a greater variety of evolu• concerning the inherent mechanisms of heredi• tionary patterns, which is only in part due to tary transmission, their emergent result as their wide geographical distribution. moulders of minor or major taxa ; that much The last chapter, entitled "The physiologic• has been made also of natural selection as a genetic species concept and the dynamics of the controlling force. But he will find that it is not evolution of species and genera" offers a con• too clear what the taxa which are used as ex• cise hut extremely lucid review of the sources of amples have become or are becoming adapted genetic variability and the means by which it to! He will also honestly have to admit that is produced. The excellent Figure 72 shows at ecologists, as yet, have hardly provided work• a glance the ''building blocks" of heredity (genes, ers in other fields with a satisfactory repertorium chromosome segments, chromosomes, genomes) , of units as manageable as the species of the tax• the process by which they operate (creative mu• onomist or the genome of the geneticist. This tation, recombination, loss, duplication., addi• task lies ahead ; now that ecospecies and eco• tion) ; and the evolutionary level on which they types are beginning to be known, it will be worth function (intra- or inter-specific). Two fur• while to project them against the smallest en• ther tables (74 and 75) offer a key to a rational vironmental units that contain them and to taxonomic hierarchy of categories based on the evaluate natural selection in terms of the kind, principles previously outlined and tested. This quantity, and durability of pressures that govern codification of the dynamic aspects of speciation their dynamics. which has now been forced to the attention of even PIERRE DANSEREAU the most conservative systematists will be most DEPARTMENT OF BOTANY, UNIVERSITY OF welcome. It seems that comparia, cenospecies, MICHIGAN, ANN ARBOR, MICHIGAN