54
H. WARIS AND P. KALLIO
a plasmatic heredity is concerned. Bünning (1953) has objected to the
application of these terms. The theoretical interpretation of the
phenomenon will be discussed in Sections X I and X I I .
Since the description of the uniradiate form of M. thomasiana var.
notata, analogous forms have been obtained from four further species,
namely M. rotata var. evoluta (Kallio, 1954), M. torreyi (Kallio, 1957,
1959), M. americana and M. fimbriata (Kallio, 1960). The uniradiate
form of M. torreyi was obtained in a culture exposed to continuous
illumination, which has an injurious effect on the cells (Kallio, loc. cit.).
I t also appeared in an old culture grown by Waris under normal conditions. In neither case did the uniradiate form of this species give rise
to viable strains. I t may be mentioned, in addition, that uniradiate
semicells can be formed at the anucleate isthmus of a double cell with a
nucleate and anucleate isthmus (Kallio, 1959).
Various characteristics of the uniradiate cells can be summed up by
the term 'hypertrophy'. These characteristics include an increase in
size (length and width), provided the lobes are formed on the same level.
However, the size is subject to great variability. In particular, when the
lateral lobes are partly or wholly duplicated on two levels the size is
often greatly reduced. In other words, the increase in the number of
wings is accompanied by a decrease in the size of the lobes. Theoretically,
the hypertrophy can be interpreted as a response of the cell to a change
in the nucleo-cytoplasmic ratio in favour of the nucleus. This conclusion
is supported by the fact that the above-mentioned characteristics of the
uniradiate forms are similar to those of the polyploid forms (Section
VIII).
B. Aradiate Cells
An aradiate form, lacking the lateral lobes on both sides, has been
obtained only from M. americana (Kallio, 1960) but is nevertheless of
particular theoretical interest (Fig. 2).
When old cultures of M. americana were exposed to continued
illumination, numerous double cells of different types were produced.
In one of the culture tubes aradiate cells were produced spontaneously.
They represent a cell type that scarcely resembles the genus Micrasterias ; according to Kallio, it shows a certain analogy with the genus
Ichthyodontum recently described by Scott and Prescott (1956). When
grown under the same conditions as the normal M. americana the
aradiate form is longer and develops polar lobes which are less well
differentiated.
The aradiate form has not been observed to revert to the uniradiate
or biradiate form, although the line has undergone thousands of cell
divisions. I t may be mentioned that in a control culture of the uni-
H. WARIS AND P. KALLIO
a plasmatic heredity is concerned. Bünning (1953) has objected to the
application of these terms. The theoretical interpretation of the
phenomenon will be discussed in Sections X I and X I I .
Since the description of the uniradiate form of M. thomasiana var.
notata, analogous forms have been obtained from four further species,
namely M. rotata var. evoluta (Kallio, 1954), M. torreyi (Kallio, 1957,
1959), M. americana and M. fimbriata (Kallio, 1960). The uniradiate
form of M. torreyi was obtained in a culture exposed to continuous
illumination, which has an injurious effect on the cells (Kallio, loc. cit.).
I t also appeared in an old culture grown by Waris under normal conditions. In neither case did the uniradiate form of this species give rise
to viable strains. I t may be mentioned, in addition, that uniradiate
semicells can be formed at the anucleate isthmus of a double cell with a
nucleate and anucleate isthmus (Kallio, 1959).
Various characteristics of the uniradiate cells can be summed up by
the term 'hypertrophy'. These characteristics include an increase in
size (length and width), provided the lobes are formed on the same level.
However, the size is subject to great variability. In particular, when the
lateral lobes are partly or wholly duplicated on two levels the size is
often greatly reduced. In other words, the increase in the number of
wings is accompanied by a decrease in the size of the lobes. Theoretically,
the hypertrophy can be interpreted as a response of the cell to a change
in the nucleo-cytoplasmic ratio in favour of the nucleus. This conclusion
is supported by the fact that the above-mentioned characteristics of the
uniradiate forms are similar to those of the polyploid forms (Section
VIII).
B. Aradiate Cells
An aradiate form, lacking the lateral lobes on both sides, has been
obtained only from M. americana (Kallio, 1960) but is nevertheless of
particular theoretical interest (Fig. 2).
When old cultures of M. americana were exposed to continued
illumination, numerous double cells of different types were produced.
In one of the culture tubes aradiate cells were produced spontaneously.
They represent a cell type that scarcely resembles the genus Micrasterias ; according to Kallio, it shows a certain analogy with the genus
Ichthyodontum recently described by Scott and Prescott (1956). When
grown under the same conditions as the normal M. americana the
aradiate form is longer and develops polar lobes which are less well
differentiated.
The aradiate form has not been observed to revert to the uniradiate
or biradiate form, although the line has undergone thousands of cell
divisions. I t may be mentioned that in a control culture of the uni-