Sporulation of Lichen Gonidia. R. Paulson 43 
much more slowly in the central body than in the other cell 
contents. By the fuchsin and bichromate of potash method this 
body is rendered colourless by thoroughly washing with water 
after staining; a pyrenoid remains coloured. The central body 
has not the distinctly semi-crystalline outline so often figured 
in drawings of gonidia. 
It has been generally assumed that the green gonidium of 
lichens, similar to that of Evernia prunastrt, increases in number 
by means of a vegetative cell-division like that observed in 
the cells of Pvotococcus viridis Ag. (= Pleurococcus of most 
modern authors), viz. by the formation of a transverse wall, 
and that sporulation takes place only after the gonidium has 
been isolated from the lichen thallus and subjected to cultural 
methods similar to those described by Famintzin, and 
Baranetzky (s),Woronin (13), Bornet (2) and recently by Chodat(3). 
The gonidium of Everma prunasivt is common to a large 
number of fruticose, foliose and crustose lichens belonging to 
the following genera. Chaenotheca, Calicium, Cyphelium, Sphae- 
rophorus, Candelaria, Parmelia, Cetraria, Evernia, Ramalina, Us- 
nea, Alectoria, Thelochistes, Xanthoria, Placodium, Candelariella, 
Physcia, Rinodina, Lecanora, Acarospora, Lecania, Icmadophilus, 
Haematoma, Pertusaria, Gyrophora, Stereocaulon, Cladoma, Le- 
cidea, Biatorella and Buellia. 
The gonidium does not multiply vegetatively as a constituent 
of the lichen thallus, but the original protoplast of the mother 
cell divides into two, four, eight or sixteen, sometimes more, 
distinctly separate wall-less masses (figs. 3 and 4). Each of 
these masses (reduced zoogonidia?) rapidly secretes a cell-wall, 
develops a chloroplast and nucleus and, in a short period, 
resembles exactly, in miniature, the mother cell as it appeared 
before it commenced to sporulate. The mother cell-wall, either 
by becoming diffluent or by bursting, sets free the daughter 
cells (fig. 5). May not the empty cells of Danilov(4) or the 
nekral layer of Elenkin be the empty cells after sporulation has 
been completed? In most cases the mother cell-wall becomes 
diffluent and the daughter cells are left together in a spherical 
group until hyphae force themselves between the daughter 
gonidia and push them farther apart (fig. 6), or, until they 
completely surround a group and bind the cells together into 
a mulberry-like mass. 
It is probable that the most active period of sporulation in 
lowland districts is in the early months of the year, February to 
April, but sporulation has been found taking place at all periods 
of the year except during prolonged drought. 
Sporulation of the gonidia of EF. prunastri is exactly similar 
to that which takes place in Chlorella vulgaris Beijer. when 
