310 
Proceedings of the Royal Irish A cademy. 
XXXV. — On a Minute Nostoc with Spores, with brief Kotice of 
RECENTLY PUBLISHED OBSERVATIONS ON COLLEMA, &0. BY WlLLIAM 
Archer. With Plate XXI. (Science). 
[Read June 24, 1872.] 
The appearance of a highly interesting and noteworthy communication 
from Professor Max Reess, conveying a description of certain novel ex- 
periments instituted by him on the growth of a Collema from the spores, 
and giving his views as to the bearing thereof as regards Nostoc,* which 
I have only just seen, recals to my recollection a seemingly remarkable, 
though isolated, example of a not uncomm^on minute aquatic Nostoc, 
with spores, brought forward by me at a recent meeting of our Micro- 
scopical Club, but not publicly exhibited, from want of time, and since 
then somehow overlooked to be recorded. 
The little Nostoc, presenting the speciality to which I am desirous 
of directing attention, is a very minute one, though the dimensions of 
the subglobose or elliptic fronds vary much. It is rather common in 
moor and certain bog pools. On account of its small size, therefore 
readily capable of compression, and its pellucid character, the elegant 
arrangement of its tortuously twisted rather large moniliform filaments, 
is often nicely seen, and this causes it to be a very pretty and favour- 
able illustrative example of its type, for examination in its entirety 
under the higher powers of the microscope. Its minute size calls to 
mind JVostoc minimum (Currey),f but in it the cells are described as 
quadrate, with a sinus at each side, lending a crenate outline to the 
filaments, and the heterocysts are large, whilst here the cells are orbi- 
eular, or for a time slightly flattened at the junctions, and the hetero- 
cysts are but slightly wider, though longer than the ordinary cells. 
This plant is probably identical with JVostoc paludosum (Kiitz.), though, 
as regards anything to be deduced from the heterocysts, Kiitzing- is 
silent. But the interesting point connected with it is a single example 
of it having presented indubitable spores," of precisely similar 
nature to those in Sphserozyga, &c., but with the peculiarity of their 
being always placed singly between two heterocysts. The pairs of 
heterocysts with the intervening spore occurred at just about the same 
intervals as in ordinary examples occur the isolated heretocysts; the 
spores large, broadly elliptic, about one-third longer than broad; their 
diameter more than twice the diameter of the heterocysts, about thrice 
the diameter of the ordinary cells; the ''bright points" of the hetero- 
cysts not very conspicuous. (See PL XXL, fig. 18). 
* Professor Max Reess : " Ueber die Enstehung der Flechte Collema fflaucesceus 
Hofftn., durch Aussaat der Sporen derselben auf Nostoc lichenoides^ Vauch." In 
" Monatsb. der k. Akad. der Wiss. zu Berlin," Oct., 1871, p. 523. 
t Currey ''On Freshwater Algse," in " Quart. Journ. of Mier, Sci.," vol. vi. 
{1st ser.), page 216. 
