50
H. WARIS AND P. KALLIO
of regularity, but minor deviations from it often occur. At any rate, the
number of lobules and dents is an important characteristic that reflects
nuclear changes as well as environmental conditions. Thus polyploidy
and aneuploidy are characterized by the number and arrangement of
the lobules. Moreover, deficiency in the power to develop lobes may be
transmitted to offspring through an indefinite succession of cell divisions.
On nuclear division the septum will always be formed at the isthmus
even if the nucleus has been displaced by centrifuging. By making use
of this fact it is possible to produce polyploid, aneuploid and enucleate
cells by centrifugation. After the septum is formed, the new semicells
appear as rounded bulges between the parent semicells and gradually
differentiate into lobes. During this process a vigorous flow can be seen
in the cytoplasm, the direction of which seems to be correlated with the
differentiation (Kiermayer and Jarosch, 1962). The expansion of the
cell has been regarded as due to a yielding of the cell wall to turgor
pressure; the local differences in expansion are then referred to the
uneven deposition of membrane substance which can be demonstrated
with M. rotata when the turgor pressure is lowered by a surrounding
solution of a suitable concentration (Jarosch and Kiermayer, 1962).
The last-mentioned authors attribute a particular significance to the
'initial deposition pattern of the membrane'. A detailed description of
the fine-structure of the cell wall in Micrasterias and other desmids has
recently been given by Drawert and Mix (1962a) with references to
earlier workers. I t appears that the initial membrane does not persist
but disappears, the persistent cell wall being of later origin. The latter
is provided with pores and these with 'pore organs', parts of which
compose the gelatinous envelope. The motility of the cell is due to the
excretion of mucilage from the pores in the polar lobes ; the movement
mucilage is not connected with the pore organs. Owing to the excretion
of mucilage the cells are capable of phototactic movement. A striking
effect making observation difficult is caused if the illumination in the
microscope is too strong, for then the cells may detach themselves from
the watch-glass and float away.
IV. Culture of Micrasterias
The general methods of cultivating algae have been described by
Pringsheim (1946, 1950). The cultivation of Micrasterias has, in addition,
been described by Waris (Waren, 1926, 1933), Waris (1950a, 1953),
Kallio (1951, 1953a, b), Pringsheim (1930), Pringsheim and Pringsheim
(1962), and Kiermayer and Jarosch (1962). The Micrasterias species,
like most of the desmids, can be cultivated in inorganic nutrient solutions, but the addition of a suitable organic chelating substance, par-
H. WARIS AND P. KALLIO
of regularity, but minor deviations from it often occur. At any rate, the
number of lobules and dents is an important characteristic that reflects
nuclear changes as well as environmental conditions. Thus polyploidy
and aneuploidy are characterized by the number and arrangement of
the lobules. Moreover, deficiency in the power to develop lobes may be
transmitted to offspring through an indefinite succession of cell divisions.
On nuclear division the septum will always be formed at the isthmus
even if the nucleus has been displaced by centrifuging. By making use
of this fact it is possible to produce polyploid, aneuploid and enucleate
cells by centrifugation. After the septum is formed, the new semicells
appear as rounded bulges between the parent semicells and gradually
differentiate into lobes. During this process a vigorous flow can be seen
in the cytoplasm, the direction of which seems to be correlated with the
differentiation (Kiermayer and Jarosch, 1962). The expansion of the
cell has been regarded as due to a yielding of the cell wall to turgor
pressure; the local differences in expansion are then referred to the
uneven deposition of membrane substance which can be demonstrated
with M. rotata when the turgor pressure is lowered by a surrounding
solution of a suitable concentration (Jarosch and Kiermayer, 1962).
The last-mentioned authors attribute a particular significance to the
'initial deposition pattern of the membrane'. A detailed description of
the fine-structure of the cell wall in Micrasterias and other desmids has
recently been given by Drawert and Mix (1962a) with references to
earlier workers. I t appears that the initial membrane does not persist
but disappears, the persistent cell wall being of later origin. The latter
is provided with pores and these with 'pore organs', parts of which
compose the gelatinous envelope. The motility of the cell is due to the
excretion of mucilage from the pores in the polar lobes ; the movement
mucilage is not connected with the pore organs. Owing to the excretion
of mucilage the cells are capable of phototactic movement. A striking
effect making observation difficult is caused if the illumination in the
microscope is too strong, for then the cells may detach themselves from
the watch-glass and float away.
IV. Culture of Micrasterias
The general methods of cultivating algae have been described by
Pringsheim (1946, 1950). The cultivation of Micrasterias has, in addition,
been described by Waris (Waren, 1926, 1933), Waris (1950a, 1953),
Kallio (1951, 1953a, b), Pringsheim (1930), Pringsheim and Pringsheim
(1962), and Kiermayer and Jarosch (1962). The Micrasterias species,
like most of the desmids, can be cultivated in inorganic nutrient solutions, but the addition of a suitable organic chelating substance, par-