74
H. W A R I S A N D P. K A L L I O
substance which takes place in the new semicells of M. rotata at 0-2 M
glucose, and attribute to it a particular significance in differentiation,
growth being regarded as due to the yielding of the new cell wall to the
turgor pressure of the vacuole.
Waris (1951) has found that in 4% glucose solution (corresponding to
about 0-22 M) the new semicells do not expand but become filled with a
gelatinous membrane substance while the cytoplasm withdraws to the
parent semicell, leaving only fine strands to connect it with the periphery
of the new semicell. If normal biradiate cells are treated in this way the
number of the strands is three, but in the case of uniradiate cells it is
two. This phenomenon has been taken into consideration in the theory
of the cytoplasmic framework (Section XII).
A peculiar formative effect is exerted when young semicells are
allowed to develop in the presence of moderate concentrations (0-084r0-100 M) of sugars, sugar alcohols and various amino acids (Waris and
Kallio, 1957). The new semicells may then form lateral lobes, some or
all of which resemble polar lobes. This phenomenon, referred to as the
'polar-type transformation of the lateral lobes', may signify that the
substances concerned promote the synthesis of materials which increase
the plasticity of the cell wall and thus even out differences in its rigidity.
The staining of the new semicells filled with membrane substance in 4 %
glucose indicates the presence of pectic substances, although the reactions are not specific for these. Thus the plasticity of the cell wall
could well be due to pectic substances. As to the possibility that the
lowering of turgor pressure plays a role in the 'polar-type transformation of the lateral lobes', it may be pointed out that the osmotic effect
was not strong enough to reduce the size of the new semicells—on the
contrary, these often grew larger than the parent semicells.
A fact of particular interest is that differentiation can be inhibited
specifically by substances such as ribonuclease, sodium 2, 4-dinitrophenol and mercaptoethanol, which may cause the new semicells to
assume shapes similar to the enucleate or to the hypohaploid cells,
although the form is subject to considerable variation (Kallio, 1963).
I t is remarkable that these substances and enucleation also affect the
behaviour of the cytoplasm and the duration of life in a similar way.
Thus the inhibition of differentiation by the removal of the nucleus
might be due to the fact that the synthesis of ribonucleic acids is
interrupted.
X I . Theory of the Cytoplasmic Framework
The study of the genus Micrasterias has led us to the view that in
cell division the continuity of the bilateral symmetry depends on
certain structural units in the cytoplasm which cannot arise de novo
H. W A R I S A N D P. K A L L I O
substance which takes place in the new semicells of M. rotata at 0-2 M
glucose, and attribute to it a particular significance in differentiation,
growth being regarded as due to the yielding of the new cell wall to the
turgor pressure of the vacuole.
Waris (1951) has found that in 4% glucose solution (corresponding to
about 0-22 M) the new semicells do not expand but become filled with a
gelatinous membrane substance while the cytoplasm withdraws to the
parent semicell, leaving only fine strands to connect it with the periphery
of the new semicell. If normal biradiate cells are treated in this way the
number of the strands is three, but in the case of uniradiate cells it is
two. This phenomenon has been taken into consideration in the theory
of the cytoplasmic framework (Section XII).
A peculiar formative effect is exerted when young semicells are
allowed to develop in the presence of moderate concentrations (0-084r0-100 M) of sugars, sugar alcohols and various amino acids (Waris and
Kallio, 1957). The new semicells may then form lateral lobes, some or
all of which resemble polar lobes. This phenomenon, referred to as the
'polar-type transformation of the lateral lobes', may signify that the
substances concerned promote the synthesis of materials which increase
the plasticity of the cell wall and thus even out differences in its rigidity.
The staining of the new semicells filled with membrane substance in 4 %
glucose indicates the presence of pectic substances, although the reactions are not specific for these. Thus the plasticity of the cell wall
could well be due to pectic substances. As to the possibility that the
lowering of turgor pressure plays a role in the 'polar-type transformation of the lateral lobes', it may be pointed out that the osmotic effect
was not strong enough to reduce the size of the new semicells—on the
contrary, these often grew larger than the parent semicells.
A fact of particular interest is that differentiation can be inhibited
specifically by substances such as ribonuclease, sodium 2, 4-dinitrophenol and mercaptoethanol, which may cause the new semicells to
assume shapes similar to the enucleate or to the hypohaploid cells,
although the form is subject to considerable variation (Kallio, 1963).
I t is remarkable that these substances and enucleation also affect the
behaviour of the cytoplasm and the duration of life in a similar way.
Thus the inhibition of differentiation by the removal of the nucleus
might be due to the fact that the synthesis of ribonucleic acids is
interrupted.
X I . Theory of the Cytoplasmic Framework
The study of the genus Micrasterias has led us to the view that in
cell division the continuity of the bilateral symmetry depends on
certain structural units in the cytoplasm which cannot arise de novo