Modular Growth Research Articles

Preface

Contributors to this Discussion Meeting were given only the most general guidance to what is meant by ‘modular’. The letter of invitation said “By ‘modular’ we imply growth of the genetic individual by the repeated iteration of (multicellular) parts - modules. This means that we can consider together at the meeting the growth and form of corals, higher plants, fungi,..., ascidians, ..., bryozoans, etc.” . Modular growth contrasts with ‘unitary’ growth, in which the zygote develops to a determinate structure that is repeated only when a new life cycle is started from a single-celled stage, usually a zygote. Of course most unitary organisms bear repeated parts, such as legs, wings and body segments, but they are formed in early embryogenesis, not by continued or prolonged somatic iteration, and their numbers are usually very strictly determinate. We might count the numbers of flies in a population of Drosophila by counting the numbers of legs and dividing by six, or of birds by counting the wings and dividing by two. There is no such determinate divisor for the genetic individual (genet) of a modular organism - no determinate number of leaves or buds on a tree, polyps on a coral, hyphae in a fungal colony or branches on a root system. Modules themselves, however, may be quite strictly determinate in form, e.g. the number of petals on a flower, the number of leaflets on a leaf.

Defensive strategies of modular organisms

Convergences concomitant with the occurrence of modular growth among systematically remote plant and invertebrate taxa not only reflect similar optimal ways of exploiting resources such as space, but also common defensive requirements among such organisms. This paper analyses the kinds of unfavourable interspecific interactions, principally predation, epibiosis, and endobiosis, which are found among the major aquatic invertebrate groups that may be considered to be modular (Porifera, Bryozoa, and some of the Coelenterata and Tunicata). Most of the organisms are also non-locomotory, and in extreme cases, virtually immotile. The defence mechanisms of organisms exhibiting the opposing traits of (i) modular and unitary organization, and (ii) motility and immotility, are compared and contrasted. There is a more widespread occurrence of defence (i) by means of consolidated and unconsolidated skeletal reinforcement, and (ii) by actively and passively dispensed secondary substances, in less motile than in more motile organisms. These defensive modes represent alternatives to ‘fight’ and ‘flight’ responses seen within the more motile invertebrates. Lack of motility is of greater significance in correlating defensive modes than is modularity. The balance between physical and chemical mechanisms used in defence can vary, even among closely related taxa. A more particular pattern of significance is the more widespread occurrence of defence by the use of passively dispensed chemical substances within modular, rather than unitary non-locomotory invertebrate groups. This may be a response to the increased risks of pathogenic infection which modular biota face through their susceptibility to frequent large scale wounding and partial mortality.

Physiological consequences of modular growth in plants

Modular plants are structurally stable systems. Perturbations in the genome that arise during growth (somatic mutations) are, it is conjectured, detected and eliminated by diplontic selection at the apical meristem. This requires accurate control, which, it is suggested, results in the accuracy of module arrangement, or phyllotaxy. During differentiation vegetative modules tend to retain autonomy and totipotency; the differentiated state is maintained by a constant flux of signals between parts. This enables damage to be repaired and differentiation to be adjusted to the availability of resources. The differentiation of modules to form flowers, on the other hand, is achieved by loss of totipotency, by hierarchical organization of the genotype, and by tissue-specific signals between parts. Elaborate, but fixed-function, structures can be produced in this way. The physiology of modular plants is best described in terms of cooperation, not competition, between modules. The theory of multicomponent systems predicts that as plants increase in size, structural stability of growth will be lost unless the connectance between modules is kept below a critical value. Experiments confirm that the exchanges of assimilate between modules are limited, but not fixed (the system can adapt to damage). The distribution system is vulnerable to exchanges that might benefit individual modules but that would reduce the inclusive fitness of the genome. Such exchanges are controlled by the organized senescence of branches, leaves, fruit and ovules.

Preface

Modular organisms are those that grow by the repeated iteration of units of structure. This manner of growth is characteristic of many invertebrates, and of higher and most lower plants. Modular organisms almost inevitably iterate their units of construction by branching. The modules may then separate from each other to become physiologically independent parts of a clone ( Hydra and duck­weeds) or remain attached to each other in more or less physiologically integrated wholes (trees, corals, salps, etc.). The ways in which the attached modules of a genet are arranged relative to each other gives the whole an often characteristic form that may, as in the species-specific outline of trees or corals, defy accurate description in words yet be modelled effectively by computer graphics. Modular growth normally constrains organisms to a fixed immobile life, though there are exceptions among free-floating aquatics. Most of the properties associated with mobility in unitary organisms are expressed through the form or architecture of modular organisms, e. g. the capture of resources, mating, competition, defence.

The Life History of Lithospermum Caroliniense, A Long‐Lived Herbaceous Sand Dune Species

Pollination, fecundity, dispersal, establishment, and survival of Lithospermum caroliniense (Boraginaceae) were examined over five years on sand dunes of different ages at Miller Dunes, Indiana, USA, to determine the effect of various environmental factors on the relationship between reproduction and other life history stages. Lithospermum caroliniense is a self—incompatible, iteroparous, distylous herb that depends on cross—pollination by insects for fertilization. Level of pollination was highly variable from year to year. For each of the two floral morphs, a high proportion of pollen was derived from the other morph in years of abundant pollination. In years when pollen loads were extremely low, fruit—set was limited by pollinator activity. Even with abundant transfer of compatible pollen, fecundity of L. caroliniense averaged less than one nutlet per flower. Individuals were consistent in level of fruit production from year to year. Emergence of seedlings of L. caroliniense was greatest when propagules were covered by 1—4 cm of sand in experimental field and garden studies. Propagules exposed on the sand surface were unlikely to obtain sufficient moisture for germination, while hypocotyls of seedlings that germinated at depths of @>5 cm were incapable of elongating sufficiently to reach the sand surface. Most propagules germinated after the first winter, but results from experimental plantings showed that many propagules remained dormant until after the second winter. First—season seedling survival averaged 7—34%, except in 1981, when frequent rainfall and moderate temperatures doubled the percentage that survived. The highest survival was among seedlings emerging near Lake Michigan or on sites with a shallow water table. Mortality of 1— and 2—yr—old plants was low. Individual plants grew faster and flowered at younger ages at sites closer to Lake Michigan. At the site closest to the lake, °83% of the 1978 cohort flowered at age 3 or 4 yr. At greater distances from the lake, most members of the 1978 cohort had not flowered by 1983. Except for some members of the 1981 cohort established near the lake, few plants in younger cohorts had flowered by 1983. In light of the slow growth rates of 1978—1982 cohorts and of many marked adults, large individuals of L. caroliniense are probably very old. Heavy nutlets typically fell within 60 cm of the parent plant. Dispersal was primarily downslope of adults, since adult foliage was lodged in a downslope direction by the time of propagule maturation; dispersal by wind or rolling was limited. Nutlets of L. caroliniense were consumed in large quantities, apparently by rodents, since the shelled remains of nutlets were common around adults. Occasional dispersal of intact nutlets by herbivores could be important in colonization of recently formed sand dunes. Although L. caroliniense is clearly dependent on newly formed sand dunes or disturbances, colonization is rare because dispersal of propagules is extremely limited. Large propagules are essential for establishment, but are not conducive to dispersal and colonization. Long adult life—span facilitates occasional colonization. Despite traits favoring establishment, seedlings suffered high mortality, except in years of abundant and evenly distributed rainfall. Since adult mortality was generally low, the life history of L. caroliniense resembles the pattern in which high juvenile mortality favors evolution of iteroparity and a long life—span. However, in contrast to species that produce a small number of offspring in any one year, the indeterminate, modular growth form of L. caroliniense means that increasing numbers of propagules are produced over the lifetime of an individual, until habitat change results in decline of adults. The combination of life—history characteristics occurring in this species argues against strict application of current life—history categorizations.

Factors impacting the evolution of office automation

This paper examines some of the market factors which will be central to the evolution of Office Automation (OA). Corporate motivation to implement OA is related to their basic goal of improving profitability. White collar worker needs are positioned in the larger context of their working environment and what is personally important to them. Based upon the substantial portion of office Worker time spent in interpersonal communications, their three leading activity areas of voice communications, meetings, and document communications are described in terms of problems with current processes and generic solutions. Due to the benefits of automating an entire business communications cycle, desirable tools are envisioned as logically integrating multiple applications and modes of communication. Future evolution, relying upon systems architectures which encourage user customization and modular growth, will increasingly provide workable systems solutions to the problems of information handling.

Continuity of vegetation in space and time: A comparison of insects' habitat templet in different successional stages

Conslusions and SummaryThis paper shows how dynamic are patterns of host plant distribution in space and time and indicates methods of assessing these features of the habitat templet that will play a major role in the evolution of the optimal migratory (sensu lat.) strategy.The actual spatial patterns of host plants vary according to the growth form, environmental tolerance and propagule dispersal of the particular species. This study was not sufficiently extensive to detect trends in these features in relation to successional age. However, the length of time the host plant remains in the same location (H in the calculation of durational stability=H/τ), increases with the successional age of habitat, as does the size of patches of hsot plants, particularly when these are due to modular growth. Therefore the probability of an insect being able to oviposit on or near the host plant on which it fed as a larva increases with the successional age of the habitat.

Simulation of a telecommunications multiprocessor switching system

The stringent real-time operating requirements of telecommunications switching systems have prompted the design of special-purpose processors that allow modular growth and provide high levels of reliabil ity, availability, security, flexibility, and capacity. One such system is the Mark II BL (MKIIBL), a telecommunications-oriented multiproces sor developed by GEC as the controller for the British Post Office's SYSTEM X. The complexity of the Mark II BL makes computer-aided design tools essential in initial design, design evaluation, per formance evaluation, and the writing of applications software. We have developed a computer-aided design package for the Mark II BL system. It is based on a simulation using the process interaction approach and is imple mented in SIMULA. We have validated the simulation by comparing the performance of simulated applica tions software for a particular digital exchange with the performance of the real system. The simulator has been used to gain insight into the detailed be havior of the system and to test alternative strate gies and design modifications. A typical result of such an investigation is reported. We conclude by mentioning some proposed extensions to the simulator and its application in design.

A Model for Chemosterilization Experiments with Special Reference to the Cabbage Root Fly (Erioischia brassicae (Bouche))

Applying comparative study on the characteristics of modular growth of five mutual species such as Stipa grandis, Leymus chinensis, Cleistogenes squorrosa, Lespedeza dahurica and Heteropappus altaicus, the grey-correlative analyses between the demographic growth analysis indexes and average temperature, precipitation and moisture had been carried out during months of the growth seasons from 1999 to 2000 in Research Stations of warm-temperate and moderate-temperate steppes of Inner Mongolia. The results demonstrated that the indexes of DRGR & DRGRa and DULA of these species were all higher in moderate-temperate steppe than warm-temperate steppe, showing the ecological characteristics of adaption themselves to the climate of shorter growth season and inadequate thermal condition, while longer duration of leaf area and modular quantity (DLAD & DMND) of these species reflected the adaption of the longer growth season and sufficient quantity of heat in warm-temperate steppe. Meanwhile, the greycorrelative degree between modular growth indexes of these species and moisture was remarkably higher in warm-temperate steppe than in moderate-temperate steppe, showing that modular growth of plant individual was more sensitive to the combination of water and heat in growth season in warm-temperate steppe, and indicating the response characteristics of plant modular growth in different thermal steppe region.

The Datran system

The Datran system is designed to serve the specific needs of the data communications user. Data communications terminals almost universally employ a digital format; therefore, an early consideration was the use of digital transmission in lieu of the analog transmission employed by most conventional common-carrier systems. The location of the potential users was examined, this having an important bearing on the transmission media selected. Growth expectancy for future years establishes the base upon which to plan the initial system capacity, the hierarchy of system subassemblies for economical modular growth, and phased construction. The employment of digital channel derivation equipment provides a high channel capacity for a given channel bandwidth as compared to analog transmission and permits the use of highly reliable integrated components at a significant reduction in channel end costs. Time-division multiplexing (TDM) switching with a stored program controller provides reliability and flexibility to meet the changing needs of the data communications user and affords significant savings in space, power, and implementation costs of conventional space-division switches.