Darwin's Observations Research Articles

A Darwinian Approach to Plant Ecology

The theory of evolution by natural selection is an ecological theory-founded on ecological observation by perhaps the greatest of all ecologists. It has been adopted by and brought up by the science of genetics, and ecologists, being modest people, are apt to forget their distinguished parenthood. Indeed, Darwinian plant ecology has been largely neglected and a changeling child nourished and brought o adulthood by Schimper and Warming who asked geographical questions about vegetation, and answered the questions by demonstrating correlations between climate and soils on the one hand and comparative physiology on the other. By contrast with the 'vegetationalist' and his concern to describe and interpret areas of land, Darwin's ecological observations and the questions he asked were based on a consideration of individuals and populations-a preoccupation with numbers. 'Look at a plant in the midst of its range, why does it not double or quadruple its numbers?' '. . . if we wish in imagination to give the plant the power of increasing in number, we should have to give it some advantage over its competitors, or over the animals which prey on it'. 'Look at the most vigorous species; by as much as it swarms in numbers, by so much will it tend to increase still further' (Darwin, Origin of Species, Chapter III).* These quotations, with their emphasis on numbers, pose problems of population biology-of a demography which has never gained a momentum in plant ecology, although it has played a vertebral role in animal ecology. Two interlinked properties of higher plants have seriously hindered the development of plant demography-plasticity and vegetative reproduction. Darwin found a 26-yearold pine tree on heathland which 'had during many years tried to raise its head above the stems of the heath and had failed'. It is clearly not fair to count such a plant as a unit equal to a full grown tree in a population census. A mature plant of an annual weed such as Chenopodium album may produce four seeds or 100 000 seeds, depending on the nutrient and water status of the soil. It can therefore be argued that a statement about numbers of plants implies very little about the real nature of the population. Vegetative reproduction is a further obstacle to census making, because the vegetative offspring remain to some extent a part of the parent, often for a long period. When is such a ramet to be counted as an individual? Arbitrary decisions have to be made if plant populations are to become numerable and the arbitrariness of the decisions has often discouraged attempts to count plants. These problems are, however, not peculiar to plants and have had to be faced in animal demography where they arise in only a slightly less acute form. Plasticity in individual size and reproductive capacity have to be taken into account in population studies of fish and even of Drosophila. Vegetative reproduction in Hydra, where the 'ramets' slowlv develon indenendence. has not Drevented its use in model population studies. * All quotations in this paper are from Chapters III and IV of The Origin of Species (1859), the text being the Everyman edition of 1928. Italics are mine. 247

The repetition of phonemic chaeacteristics in radical morphemes in sets of synonyms from indo-european languages*

The next two notional groups to be examined in our inquiry investigating the correlation between sound and meaning are the group narrow, knead, thick (in density), and the group touch, stretch, put. The first contains in its radical morphemes a much greater number of nasal phonemic characteristics than expected from the Representative Sample. The second one presents the case of an unusual accumulation of dental phonemic characteristics. These groups have been established by the same method of selection of synonymic sets from Buck's dictionary employed already for the groups smooth and rough, and they have also approximately the same size. The hypothesis of a physiologically founded sound symbolism has been the criterion for constituting our groups here and there. In the same way as we quoted Plato's view of a natural connection between I and smoothness and between r and roughness, we can for the sound·symbolism of dentals appeal to the frequent - acoustically unexplained - appearing of these phonemes in the so-called »echoic« verbs and interjections for touching; striking, and falling, and on the other side to a largely accepted view of the correlation between the gesture of indicating (stretching the arm, the finger) and the use of »centrifugal« dentals in demonstrative and personal pronoums. Similarly the »centripetal« expressivity of nasals - on the physiological basis of tactile and proprioceptive sensations from the combined pressure of the muscles of (lips,) tongue and soft palate - has been repeatedly emphasized by linguists and psychologists. Darwin's observation in his treatise The expression of emotions about the involuntary accompaniment of the movements of the hands and the movements of the organs of speech can be considered as a supplementary clue of explanation being valid in both cases.

Local Variation in Habits of the Lizard, Amblyrhyncus cristatus

ON a recent visit to the Galapagos Archipelago I noticed a point concerning Amblyrhyncus cristatus, an aquatic species, which might be of interest as a footnote to Darwin's observations on the same reptile.

Observations on the Attachment of Balanus crenatus Bruguiere Found in the Waters of Puget Sound

It would appear from Darwin's observations upon adult barnacles and those of the writer during the stage of metamorphosis and the process of attachment of B. crenatus Bruguiere that the prehensile antennae of this species were attenuated. Verification for the contention is obtained from the historical data reported by collectors as to the scarcity or absence of the species on arid and rocky beaches, contrasted with its abundant occurrenee where submerged by the tide during its first few hours of attachment. The early development of the cement glands may be to overcome the buoyancy of the water, while the cypri are in their natural habitat; or the ample supply of water may favor the abundant supply of gelatinous material. References in the literature to the recovery of B. glandula Darwin from any stated depth of water are lacking. Camera lucida drawings were made of the Cyclosa of B. crenatus Bruguiere which had been secured to glass slides during their early metamorphosis into the attached barnacle. Thanks are due to Lieutenant E. W. Sylvester, of the U.S. Navy, for his many courtesies during the experimental work; and to Mr. Henry A. Pilsbry, special curator of the department of Mollusea, Academy of Natural Sciences, Philadelphia, who identified the two species submitted to him from adult barnacles taken from the experimental Norfolk Standard steel plates, and from rocks along the shore of Alki Point; to Professors Trevor Kincaid and John Guberlet, of the zoology department of the University of Washington, for their kindness in reviewing the microscopic specimens and data; to Ernest C. Angst, who made the free-hand drawings of the cypri of B. crenatus Bruguiere.

Dehiscence of the Capsules of Collomia

IN Mr. Duthie's very interesting account (vol. xii. p. 494) of the mode of dehiscence of the capsules of this plant, he suggests that the purpose of the projection of the seeds on to the viscid hairs of the plant itself may possibly be found in its enabling the plant to live on its own seeds. Surely this is a superfluous and needlessly improbable hypothesis. The violent discharge cf the seeds is undoubtedly one of the modes adopted by nature for their dispersion to plots of ground where the mineral constituents of the soil which they mainly require have not been entirely used up by the parent plant. Their interception by the parent plant is no doubt accidental. The purpose served by the viscid hairs of this and other plants still remains to be discovered if we follow the clue afforded by Mr. Darwin's observations on insectivorous plants. The violent expulsion of the seeds from the ripe capsule is a much more common phenomenon than that which we have exhibited in Collomia, together with a few other plants, as Acanthus, Ruellia, Eschscholtzia, and Geranium, where the whole fruit is thrown off together. Mr. Duthie will find a good description of the phenomenon in Hildebrand's “Die Schleuderfruchte und ihr im anatomischen Bau begrundeten Mechanismus,” in Pringsheim's “Jahrbunh” for 1873–74. The author draws an interesting comparison between the structure of Collomia, with its single seed in each division, and its apparatus for projecting these to a distance, and that of the allied genus Gilia, with its numerous seeds in each division, which possess no such mechanism, but which, being much lighter, are consequently more easily dispersed by the wind.