Summary.A summary of the investigation may be made by reference toC/adonia digitata, var.denticulataAch. = var. monstrosaNyl., the lichemwhich has been used as material for many of our preparations,1The gonidium is spherical except when subject to pressure from other gonidia. The diameter of fully developed cells ranges from 8 to 15 μ.2The chloroplast, in the mature gonidium, has a slightly uneven surface.3After fixing and staining, minute reticulation of the cytoplasm is evident.4The 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.5A 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 eentrosome.6Twin gonidia frequently occur.7There is no vegetative cell division of the gonidium.8The increase in the number of gonidia results from the formation of daughter gonidia, autospores (reduced zoogonidia).9We have seen no penetration of gonidia by