PROTOPHFTA. 247 
(Fig. 165), which divide in all directions, the latter imbedded in a stratified jelly; 
Gloeotbece, imbedded in a stratified jelly but dividing in one direction only; and 
Merismopedia, the cells of which divide cross-wise in a single plane. 
2. The NostocaceaB form lumps of mucilage or gelatinous pellicles which float 
in water or lie on damp earth or among moss. In the jelly are serpentine moniliform 
rows of roundish cells, a few larger cells, termed Hetero- 
cysts, the contents of which are of a different colour, being 
interposed at intervals. The filaments increase in length 
by the division of the individual cells, thus constantly 
adding to the coils which lie in the jelly that they ex- 
crete. New colonies are, according to Thuret^, formed 
in the following manner : — The jelly of the old colony 
becomes softened by water, the portions of the threads 
lying between the heterocysts become detached, separate 
from the jelly, and straighten themselves, while the hetero- 
cysts themselves remain in the jelly. After they have 
entered the water, the old portions of the threads become 
endowed with motion like the Oscillatorieae, and their exit 
is probably caused by this movement''^. The roundish 
cells of the filaments grow transversely, i.e. at right 
angles to the axis of the filament, and then divide, the division-planes being parallel 
to the axis of the filament, which now consists of a series of short articulate threads, 
the axis of whose growth is at right angles to its own. The threads which are thus 
formed increase in length and join, placing their terminal cells in contact [alternately 
above and below in each successive thread], and thus unite into a single curved 
iVoj/or-filament. Individual cells, apparently without any definite law, become hetero- 
cysts. In the meantime the gelatinous envelope is developed, and the new colony, 
which is at first microscopic, attains the size of a walnut^. 
3. The Oscillatorieae consist of rigid cylindrical filaments of various thickness, 
often extremely slender, divided into disc-like cells by very delicate transverse septa. 
The filaments are not straight, but somewhat coiled in the form of a very oblique 
spiral ; they revolve on their axis, and become matted, when large numbers grow 
together (in water or on moist earth), into balls or pellicles. When a lump is placed 
in water or on wet paper, Nageli has shown that it assumes a star-like arrangement 
in consequence of these movements. 
4. The RivularieaB ^ form soft greenish blue lumps of jelly which swim about in 
stagnant water or grow attached; in the first case they are spherical, in the second 
hemispherical, the smallest about § millimetre in diameter, the largest the size of a 
hazel-nut. A number of moniliform filaments consisting of roundish cells lie in the 
^ Thuret, Observations sur la reproduction de quelques Nostochinees, Mem. de la soc. imp. 
des sei. nat. de Cherbourg, vol. V. 1857. [Ann. and Mag. Nat. Hist. 1858, vol. II.] 
^ These motile threads of Nostoc were seen by Janczewski to enter the young stomata on the 
lower side of the thallus of Anthoceros Icevis, where they further develope into round balls. Such 
colonies of Nostoc have been known for a long time in cavities and in the tissues of different Hepa- 
ticae {Blasia, Pellia, Diplolcena, Aneura, Riccia), but have generally been considered endogenous 
gemmoe of these species, until Janczewski proved their true nature. Nosfoc also establishes itself in 
the large porous cells of the leaves of Sphagtimn. The entrance of Nostoc into the parenchyma 
of the stem of a dicotyledonous plant, Gmmera, is brought about, according to Reinke, in a different 
manner ; the deeper-lying parenchymatous cells of the outer part of the stem, themselves covered by 
layers of parenchyma, are densely filled v/ith colonies of the Alga. (Bot. Zeitg. 1872, pp. 59 
and 74.) [See also Ann. des Sc. Nat. 1872, p. 306, and Quart. Journ. Micr. Sc. 1873, p. 369.] 
^ [Archer has described the occurrence of 'spores' in Nostoc paludosum which were always 
placed singly between the heterocysts. Quart. Journ. Micr. Sc. 1872, p. 367.] 
^ De IJary, Flora, 1863, ?• 553- 
