SHELL COLOUR IN CALLIOSTOMA ZIZYPHINUM (L.) FROM STRANGFORD LOUGH, N. IRELAND

Shells of Calliostoma zizyphinum taken from Strangford Lough,N. Ireland are divisible into three distinct colour forms: white(=var lyonsi) intermediate (a pale variegated form) and purple(a dark variegated form). The predominance of white and paleshelled individuals within and the absence of white Calliostomaoutside the lough was confirmed. The proportions of animalswith white and variegated shells at selected sites were almostidentical with those previously documented, suggesting a temporalstability of colour form ratios. No differences in shell thicknessand pedal adhesion were demonstrated between these forms. Snails with white shells reflect radiant heat better, have lightercoloured feet, move more rapidly, show a greater incidence ofshell repair and are more frequently exposed on weed at lowtide, than those with either intermediate or purple shells.Increased proportions of white individuals may be associatedwith high population densities. Under such circumstances, itis suggested that increased mobility may, by increasing dispersion,reduce intraspecific competition. In the event of exposure atlow tide a white shell would help minimize thermal stress. (Received 9 February 1987;     

Does 3-Methyleneoxindole Possess Auxin Activity?

Extensive xylem differentiation was induced in explants of lettucepith parenchyma cultured for 7 d on Murashige and Skoog's mediumcontaining exogenous auxin and cytokinin. Xylo genesis was notobserved by employing various concentrations of 3-methyleneoxindole(MOl) as the source of exogenous auxin. Samples of MOI fromtwo research laboratories were tested in these studies. Trachearyelements were formed in profuse numbers in explants transferredto an IAA-kinetin medium after having been cultured for 7 don an MOI-kinetin medium. Media containing ethylenediaminetetraaceticacid (EDTA) were inhibitory to xylogenesis whether the auxinemployed was IAA or NAA; thus the response was considered notto arise from the chelation of manganous ions involved in theenzymatic oxidation of IAA. Xylogenesis was either unaffectedor inhibited by the addition of chiorogenic acid to the medium.