THE DISTRIBUTION AND MOBILITY OF THE PHYCOBIONT IN THE THALLI AND APOTHECIA OF USNEA-AURANTIACO-ATRA JACQ

Phycobionts of the lichen Usnea aurantiaco-atra Jacq. move from apothe cia to thalli, or vice versa, according to the light gradient. When th e thallus receives high light intensities while their apothecia are ma intained in the dark, the ratio of thallus/apothecial chlorophyll incr eases from 0.50 to 1.0. Likewise, the algal population in the thallus significantly increases with a concomitant decrease in the number of a lgal cells in the apothecia. The moment of algal cells inside the thal lus may be related to the absence of intracellular haustoria in this l ichen. Periparietal haustoria have been observed.