217 
Studies on Cyanopliyceae. 
published during the years 1878-1882/ besides considering the 
general morphology of the vegetative structure, describes the spores 
of a number of genera in detail and also gives data concerning 
their development and ultimate fate. Brand has also done work in 
this direction and was the first to discover the spores of Gloeocapsa 
alpinn, Naeg. 2 and of certain species of Nostoc (N. commune , N. 
microscopicum, N. muscorum ). 3 
The details of the spore-development in Anabaena will be 
described elsewhere 4 and a brief recapitulation will suffice here. 
The spores were developed very abundantly in the material of 
Anabaena Azollae, Strasburger, which formed the subject of my 
investigations. Cells about to develop into spores—I have termed 
them sporogenous cells—exhibit two well-marked integuments at 
an early stage. The inner one of these (inner integument) com¬ 
pletely envelopes the protoplast; it is colourless and apparently of a 
more or less gelatinous nature. The outer one (cell-sheath), which 
becomes more and more pronounced as the spore matures, takes the 
form of a hollow, more or less cylindrical sheath, surrounding the 
inner investment; it is individual to each cell, the transverse walls 
of the filament being constituted by the inner investment only. As 
the sporogenous cells approach maturity they become separated 
from one another by the formation of intermediate mucilage, while 
the cell-sheath closes round the open ends of the spore, forming a 
complete (always ?) outer investment or exospore. The observations, 
described in the second article of this series, seem to show that the 
two investments are present at a very early stage and merely attain 
a more distinct differentiation as the spore matures. However, if 
either of the two membranes is a newly formed structure it is 
certainly the exospore (cell-sheath), which is very difficult to dis¬ 
tinguish in early stages. 
The formation of the spores in the case in question was almost 
invariably centrifugal, i.e. spore-formation commenced in cells 
distant from the heterocysts and gradually advanced towards them. 
It is customary to unite certain species, otherwise resembling 
Anabaena, but which have centripetal spore-formation, in the sub- 
1 Nuovo Giornale Botanico Italiano, Vols. 10, 11 and 14. 
2 cf. Brand, Der Formenkreis Ivon Gloeocapsa alpina, Nag. Bot. 
Centralbl., Vol. lxxxiii., 1900, p. 228, Figs. 6-9. 
3 Brand. Morphologisch-physiologische Betrachtung iiber Cya- 
nophyceen. Beihefte z. Botan. Centralbl., Bd. xv., Heft 1, 
1903, p. 36. 
cf. foot-note 1 on page 216. 
