262 
W. J. Hodgetts. 
The dead intercalary cells which were generally present at the 
point in the filament where the false-branches arose, are thus 
curiously analogous to the heterocysts of Tolypothrix and Scytonema, 
in the relation which they bear to the false-branches. The closest 
resemblance is to Tolypothrix , where the pseudo-branches arise 
singly and the heterocysts are seriate ; occasionally, however, in 
the Prasiola the pseudo-branches arose in pairs, one on each side 
of the dead intercalary cells, thus recalling Scytonema. 
Several writers have described the occurrence of dead, 
flattened or biconcave, cells in filaments of the Hormidium- state of 
Prasiola crispa. F. E. Fritsch, 1 for example, described and figured 
such dead cells in specimens of the Alga from the Antarctic, and 
the dead cells mentioned above in the Warley material appear to 
be similar to those described by this author. 
Occasionally no sign of dead intercalary cells could be seen at 
the point of origin of the pseudo-branch, and in several cases it 
was distinctly seen that the latter was given off at a place in 
the filament where no dead cells were present. Possibly the 
development of these pseudo-branches in Prasiola may be explained 
by the Alga having gone through a short period unfavourable to 
growth, which resulted in certain intercalary cells being killed, and 
their contents disorganised, 2 while, favourable conditions again 
ensuing, the filaments later resumed active growth and produced 
the pseudo-branches at places of weakness in the filaments. 
The apices of the pseudo-branches always consisted of 
somewhat narrower and thinner-walled cells, obviously in process 
of active division and growth. The “branches” were generally 
short (rarely more than 25 cells in length) but doubtless given 
favourable conditions they might have grown much longer. 
Examination of Prasiola crispa from other localities, and at 
different times, has resulted in the finding of only isolated examples 
of this false-branching. It seems that the conditions required to 
produce the pseudo-branches in abundance are only locally or 
occasionally realised, so that their production is perhaps to be 
looked upon as a somewhat abnormal phenomenon. 
IV.—Sexual Reproduction of Chlamydomonas variabilis. 
The gametes of this species of Chlamydomonas do not appear 
to have been hitherto observed, or at any rate described. Wille 
1 Freshw. Algae in Nat. Hist. Report, Brit. Antarctic Exped., 1910, Bot. 
Pt. 1, 1917. 
2 Or these cells may have been killed by some parasite. 
8 Wille, N., Algolog. Notizen, XI. Uber die Gattung Chlamydomonas, 
Nyt Mag. f. Naturv. XLI, 1903, pp. 109-162, 
