RELATION BETWEEN THE ALGA AND FUNGUS OF A LICHEN. 501 
arrived at as to the exact shape of the chloroplast of the alga frequently 
associated with many foliose and fruticose lichens, and referred to by them 
as Cystococcus humicola, Nüg. 
Elfving (5) in describing Jrernia furfuracea, Ach., says, “the gonidium 
contains a hollow spherical chloroplast cut into on one side," but the illus- 
trations in his paper “ Untersuchungen über die Flechtengonidien," 1913, 
do not make this ** cut into one side " at all conspicuous. 
There is no vegetative division of the gonidia that we have examined, but 
increase in their number results from the production of daughter gonidia 
(reduced zoogonidia) formed by the division of the protoplast into 4, 8, 16, or 
32 masses. Frequent numbers are 8 and 16. Division seldom stops at 4 
and rarely exceeds 16 (Pl. 21. Phot. 1, d.y.). It has not been possible, so 
far, to follow the division of an individual protoplast, but in sections of 
material where the formation of daughter gonidia was actively taking place at 
the time of fixing, various stages, from the commencement of changes in the 
mother cell to the formation of the daughter gonidia, are represented. The 
newly-formed cells rapidly become spherical, secrete a cell-wall, develop a 
conspicuous so-called pyrenoid, and exactly resemble in miniature a mother 
cell. The wall of the mother cell is absorbed, for we can trace no rupture 
of the cell-wall to allow of the escape of daughter gonidia. The empty 
gonidial cells, which always occur in varying quantities in a lichen thallus, 
cannot be regarded as those from which daughter gonidia have escaped, for 
these latter remain in the original groups after the mother cell-wall has 
entirely disappeared, and it is the growth of hyphe between and around the 
newly-formed gonidia that forces them apart or binds them together into 
irregular masses. The empty and partially empty cells are the result of the 
disorganization of the protoplast, but such change is not by any means due 
only to the effect produced by the penetrating hyphal filaments. The whole 
of the contents of a gonidium may be absorbed, normally, without any 
apparent penetration of the cell-wall. Under the conditions in which 
gonidia exist death frequently occurs, it would appear, owing to the great 
number of gonidia produced at the time of sporulation, and to the con- 
sequent erowding together and lack of air. Daughter cells are often 
abortive before the mother cell-wall has disappeared. 
We have not found a nekral layer such as Hlenkin (4) figures in 
sections of Acarospora glaucocarpa and Lecidea atrobrunea, but we have 
seen a relatively small percentage of dead cells after using Chlor-Zine- 
Iodine, which makes them stand out very distinctly from the living gonidia 
and hyphz. Danilov states that the substance in partially empty cells is 
fungoid, that is, it represents the fine hyphal filaments that penetrated the 
living protoplast and absorbed its substance. It is true that the sub- 
stance within a partially empty cell sometimes stains blue immediately on 
the application of an aqueous solution of methyl green, as does the proto- 
