The Relation between the Alga and Fungus of a Lichen.

Abstract

A summary of the investigation may be made by reference to Cladonia digitata, var. denticulata Ach. = var. monstrosa Nyl., the lichen which has been used as material for many of our preparations. The gonidium is spherical except when subject to pressure from other gonidia. The diameter of fully developed cells ranges from 8 to 15 μ. The chloroplast, in the mature gonidium, has a slightly uneven surface. After fixing and staining, minute reticulation of the cytoplasm is evident. The so-called pyrenoid (nucleus) is large and central and exhibits a distinct structure throughout the substance. Its diameter is roughly one-third that of the chloroplast. A small lateral body surrounded by a light area stains darker than the so-called pyrenoid; it is very conspicuous in many of the preparations; it probably represents the centrosome. Twin gonidia frequently occur. There is no vegetative cell division of the gonidium. The increase in the number of gonidia results from the formation of daughter gonidia, autospores (reduced zoogonidia). We have seen no penetration of gonidia by hyphæ.