Length changes of growing apices of eulittoral Fugales during drying and soaking

The length changes of growing apices of Pelvetia canaliculata (L.) Dec. et Thur., Fucus spiralis L., F. vesiculosus L., F. serratus L., and Ascophyllum nodosum (L.) Le Jolis, due to drying and soaking are measured in very short intervals by use of laser diffraction. The length decrease is linear during periods of at least one hour and for the different species the decrease rate corresponds to the normal zonation of the algae; the species living highest up on the shore having the smallest rate. When soaked after one hour of drying, the length of all species increased rapidly and at approximately the same rate. Evidence is also given that considerable length growth takes place when the algae are exposed to air, increasing with increasing irradiance.