A Critical Study of certain Unicellular Cyanophyceae 91 
Scytonemaceae the sheath was found to contain cellulose, probably 
in a combined state, since it was insoluble in Schweitzer’s solution. 
These cellulose-containing envelopes of Scytonemaceae must not be 
confused with those of Petalonema and species of Lyngbya which also 
give a blue colour with zinc chloriodide and similar iodine reagents. 
For the reaction in these latter is due to a pigment, scytonemin, that 
can be dissolved out by means of eau de Javelle. 
In 1910 a short account of the mucilage of one hundred and fifty 
Algae was given by Virieux(i 7 ). Of the Cyanophyceae examined 
Chroococcus turgidus (Kuetz.) Naeg. and certain species of Phor- 
midiurn were found to have purely pectic sheaths. The results of 
Lemaire were verified with respect to the presence of schizophycose 
and cellulose in association with pectic substances in some of the 
filamentous forms, whilst certain membranes, e.g. those of Schizo- 
thrix, were found to be composed of pure cellulose. Virieux found 
callose in Hydrocoleum heterotrichum, whilst he also records schizo¬ 
phycose as occurring in Glceocapsa. 
An examination of the mucilage of Glceocapsa caldariorum Rabenh. 
and of several unidentified species of the same genus, of Microcystis 
ceruginosa Kuetz., M. flos-aquce (Wittr.) Kirchn., and Merismopedia 
elegans A. Br. show them to consist almost entirely of pectic sub¬ 
stances. They stain with basic anilin dyes and will absorb safranin, 
methylene blue and others from dilute solution. With formalin-fixed 
material safranin gives an orange, methylene blue a violet tinge. 
They are not stained by anilin blue, Congo red or eosin, nor do they 
react with zinc chloriodide and other similar iodine reagents. 
Methyl violet stains more or less strongly. They are dissolved in 
strong chromic acid. 
It would seem that the secretion of mucilages of pectic substances 
is a primitive character. In the higher plants the first stage in mem¬ 
brane secretion is the formation of pectoses, giving the middle- 
lamella of tissue-cells. This, however, is soon superseded by the pro¬ 
duction of celluloses and then, generally at a somewhat later stage, 
of other substances. If we assume that in the lower plants such as 
the Cyanophyceae, this ontogenetic series is represented by a phylo¬ 
genetic one, then the Chroococcaceae would take the most primitive 
place in such a series. 
The question of mucilage secretion naturally leads over from a 
consideration of the properties of the individual cell to the charac¬ 
teristics of the colonies formed by the adhesion of these units into 
larger aggregates. Here, as w'ould be expected from the above re- 
