GROWTH AND DEVELOPMENT IN CULTURE OF ORTHOTROPIC RHIZOMES OF POSIDONIA-OCEANICA

Orthotropic rhizomes sampled from Posidonia oceanica meadows at depths of between 3 and 4 m off Corsica and Golfe Juan, France, were cultivated for 2 years under laboratory conditions comprising natural lighting and temperatures of 18-22-degrees-C. Mortality was high only near the beginning of the experimental period, reaching 59% after 7 months, but falling to 5% over the following 18 months. Mortality appears to have been induced by bacterial growth spreading from the point of scission to infect the terminal meristem. The surviving transplants presented scar calluses near the point of scission. Adaptation was manifested principally by a change from vertical to horizontal growth accompanied by the development of adventitious roots and lateral branching of the axes as well as by abundant leaf formation in each apex. From the date of transplantation into culture, two changes occurred: leaf thickness increased generally while the amplitude of a seasonal rhythm in leaf thickness became smaller than in the sea. These two changes may have been induced by the relatively stable temperature in culture. Difference between transplants from Corsica and those from the continent in the development of both their adventitious roots and lateral branching can be explained only by differences in the age or hereditary characteristics of the respective populations.