86 
F. E. Fritsch. 
observations confirmed or supplemented Dr. Brand’s and I have 
therefore decided to publish these at once and make them the 
starting-points of the present series. 
I.—Some Points in the Structure of an Anabaena. 
N the above-mentioned material a species of Anabaena occurred 
in all stages of development and almost at once attracted 
my attention by the abundant occurrence of heterocysts. The only 
distinction between Anabaena and the closely-allied genus Nostoc is 
to be found in the absence of a common gelatinous investment round 
the colonies of the former ; Hansgirg is right in my opinion in not 
regarding this distinction a generic one (cf. Hansgirg ’84, p. 13) and 
in referring Anabaena to Nostoc as a sub-genus. 1 The two genera 
are maintained in Engler-Prantl by Kirchner (’98, p. 72), as also by 
Cooke (’84, pp. 224 and 234) and Wolle (’87, pp. 278 and 285). 
A third genus Sphaerozyga, characterised by a centripetal develop¬ 
ment of the spores with reference of the heterocysts, is now almost 
generally regarded as a section of Anabaena (Hansgirg’84, p. 13, 
’92, p. 69 ; Kirchner ’98, p. 74.) 
The species, 1 am about to describe, belongs to Anabaena 
proper, i.e. there is no common investment, although each filament 
is surrounded by a fairly broad sheath of highly transparent mucilage; 
this is generally quite evident in young stages and (Kleinenberg’s) 
haematoxylin stains it dark blue at all times. The ordinary vege¬ 
tative cells vary very considerably in size, shape and colouration. 
The young moniliform filaments are composed of relatively small 
spherical cells, more or less flattened at each end, and frequently 
having a very dark green (pale slate-green) colour; these young 
filaments are often very much convoluted (sometimes in a spiral 
manner), although almost perfectly straight ones are no rarity. 
These latter do not generally attain so considerable a length as the 
convoluted ones; and the appearance, assumed by the latter is 
probably due to the abundant cell-division, which has taken place. 
All transitions from these small spherical cells to larger oblong ones 
are to be found and both types are not rarely to be met with in the 
course of the same filament (cf. fig. 1); these larger and older cells 
generally have the typical blue-green colouration. In the large 
1 In his Prodromus however (Hansgirg ’92, pp. 56 and 67) the 
two genera are maintained, although reference is made to 
the earlier paper in a foot-notQ. 
