JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Ecology. SUMMARY(1) Analysis of more than one-hundred plant species has shown certain consistently-recognizable biological age states in their ontogeny. These are called seed, seedling, juvenile, immature, virginile, reproductive (young, mature and old), subsenile and senile.(2) Each age state may be characterized by a particular combination of quantitative and qualitative features. Qualitative features used to define the various age states are: the manner of nutrition, the type of growth, the pattern of branching of the root and shoot systems, leaf form, the presence of a particular type of shoot, the ability to reproduce by seeds, the balance between living and dead structures, and the balance between actively-growing and fully-formed structures.(3) Quantitative characteristics change uninterruptedly during ontogeny, and as a rule follow a unimodal curve.(4) Age states of species representative of a variety of growth forms have been distinguished and described. These include trees, shrubs, semi-shrubs, low semishrubs, firmand loose-tussock plants, and the following categories of perennial herbs: long-and short-rhizomed, root-suckering, stoloniferous, bulbous, tuberbulbous, tuberous and tap-rooted.(5) On the basis of these age-state studies, three main types of ontogeny in polycarpic plants are defined, using as characterizing features architectural changes of the individual plant, the form and timing of break-up of the individual plant, and the extent of rejuvenation.

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Prolactin participates in the regulation of liver function. However, prolactin receptor (PrlR) expression and its regulation have been described only for hepatocytes. In this study, we investigated the expression and regulation of PrlR isoforms in the other important intrahepatic cellular compartment: the biliary epithelial cells, or cholangiocytes. Our aim was to determine whether prolactin should be considered as a potential regulator of cholangiocyte function under normal and pathological conditions. Cholangiocytes and hepatocytes were differentially isolated from rat liver. PrlR expression was analysed at the mRNA level by isoform-specific semiquantitative PCR, and at the protein level by immunostaining of liver sections. Hormonal regulation of PrlR expression was evaluated by comparing intact rats with gonadectomized, pituitary-grafted or bromocriptine-treated animals. Common bile-duct ligation was used as the experimental model of cholestasis. Our results demonstrate that the expression pattern and regulation of PrlR isoforms is totally different in cholangiocytes compared with hepatocytes: (1) mature rat cholangiocytes express low levels of PrlR, while it is very high in hepatocytes, (2) only the long isoform is detected in cholangiocytes, while the short isoform predominates in hepatocytes and (3) PrlR levels in cholangiocytes are induced by obstructive cholestasis, but not by sex hormones or prolactin, while it is the opposite in hepatocytes. From these data, the actions of prolactin on liver are anticipated to exhibit strong cell-type specificity in both normal and pathological conditions.

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