The Origin and Development of the Apothecium etc. 
383 
where the spermatia are borne and tliere fusion of trichogyne and sperma- 
timn takes place. 
The material used in tliis work is the same as tliat which I used for 
the results described in my former paper. It was obtained from a sand- 
stone cliff overlooking Lake Mendota and from the bluffs along the Wis- 
consin River near Lone Rock, Wisconsin. Since I had found the re- 
productive structures of this Wisconsin form of Collema pülposum (Bernh.) 
Ach. to differ so mueh from wliat Stahl and Sturgis described for the 
same species, I gave a full description of my material in my previous 
paper. In the same paper I described in detail the methods used for 
fixing, embedding and staining. 
Observations. 
The thallus of Collema pulposum as seen in section is composed of 
a loose network of anastomosing fungal hyphae embedded in the jelly 
of the algal symbiont, Nostoc. To make the presentation of the subject 
as clear as possible, I have reproduced from my earlier paper a diagram- 
matic representation of a section of the thallus (Fig. 1, PI. XXX). The 
Xostoc filaments are much more abundant near the surface of the thallus, 
but are also scattered throughout its entire thickness. In unstained 
sections, the vegetative hyphae are hyaline filaments with their nuclei 
and the denser parts of their cytoplasm appearing as bright refractive 
areas. With the exception of the nuclei, the hyphae stain lightly. The 
hyphae branch repeatedly but irregularly and sliow much anastomos- 
ing (Figs. 3 — 5). In case several branches arise close together, the parent 
hypha is usually somewhat swollen near the place of origin of the bran- 
ches. The cells vary eonsiderably in size. I have found them from 1,5 
to 3,5 microns in diameter and as much as 30 microns long. Except in 
some of the smallest cells, in which growtli is apparently most rapid, 
the cytoplasm is not dense; it is usually spongy with large vacuoles, and 
occasionally somewhat granulär. In small cells tliere is always but one 
nucleus (Fig. 12); in larger cells two nuclei are quite commonly present 
(Fig. 8). This binucleate condition results from the tardy formation of 
the cross wall after nuclear division. 
The resting nuclei stain very clearly. Eacli has a single nucleole, and 
the ehromatin, connected by fine linin threads, is distributed throughout 
the nuclear cavity in the form of masses of various size (Figs. 2 — 8). 
The nuclear membrane stains lightly. Because of the small size of the 
nuclei — 1 to 2,5 microns in diameter — the details of nuclear division 
are not clear. The spindle is at first intranuclear, but by the time it is 
