102 
B. Muriel Bristol. 
production of spores directly from the juvenile cells is possibly the 
outcome of the same conditions. 
Anabcena laxa (Rabenh.) A. Br. (?) 
In the cultures of the two Broadbalk samples collected in 1881 
and 1869 an alga appeared which agrees in its characters much 
more nearly with A. laxa than with any other described form. The 
filaments are straight or slightly curved, usually single, and invested 
with a colourless sheath that is most distinct in the region of the 
spores. The vegetative cells are barrel-shaped, mostly 4—5/x broad, 
and about the same length or a little longer. Heterocysts have 
not been found, but as no mention of them is made either by 
Lemmermann' or by Tilden 2 this appears to be a very general 
character of the species. The spores are cylindrical or somewhat 
oval in shape and vary in length from 14-20/a; they differ, how¬ 
ever, from those previously described in being mostly from 7-9/a 
broad instead of only 6/a. They are produced either singly or in 
series, as many as six being frequently seen in a series. 
Anabcena oscillarioides Bory forma. 
In all of the Broadbalk soils, with the exception of the 1881 
sample, forms of this species have been found, but their deviation 
from the original description is so marked and so constant that it 
has been decided to include all of the forms except that from the 
1868 sample in a new variety of the species. The form from the 
1868 sample resembles the typical form in all respects except the 
size of the heterocysts which are only 4‘5-5/a in diameter, but a 
.diminution in the size and frequency of the heterocysts appears to 
be a character common to many soil forms grown in cultures, and 
is therefore not to be regarded as of specific importance. The 
vegetative cells are barrel-shaped, 4'5-5/a broad and about the same 
length; the spores are cylindrical 8-9/a broad and 17-21/a long. 
When ripe they have a smooth yellowish-brown wall. 
Var. terrestris nov. var. 
In mode of growth and general characters this variety agrees 
with var. tennis Lemm. rather than with the typical form. It 
possesses, however, distinctive characters which are constant not 
only in the cultures of these old soils but also of a number of recent 
soils that have been dried and set up in cultures within six 
weeks of the date of collection. The filaments grow singly, or a 
' Loc. cit., p. 181. 
* Tilden, J. Minnesota Algae I, p. 192, 1910. 
