The rhizoids of Polysiphonia lanosa

Abstract

Polysiphonia lanosa (L.) Tandy, a red alga (family Rhodomelaceae) epiphytic upon Ascophyllum nodosum (L.) Le Jolis and occasionally upon species of Fucus L., has been shown to have both a primary sporeling rhizoid and secondary rhizoids that may arise from either pericentral or central cells. Rhizoids were examined live after dissection from the host tissue. Considerable variation was found in rhizoid form and structure. Many rhizoids become complex by the penetration of additional rhizoid-like extensions from other pericentral or central cells into the originally simple rhizoid. In a small proportion of rhizoids examined, a protoplasmic protrusion was found to extend through the rhizoid wall near the apex, but there was no evidence that this formed any haustorial connection with A. nodosum cells. Excised fragments of P. lanosa cultured in close association with pieces of A. nodosum reestablished superficial contact with the A. nodosum plants by growth of new secondary rhizoids, but these did not penetrate the host tissue.