68
H. W A R I S A N D P. K A L L I O
cumulative effect of nuclear quantity on morphology is seen. The cell is,
however, almost always smaller in size than the diploid form.
Triploid cells are sometimes produced from binucleate complex cells
of type II (cf. Section VII) when three of the four daughter nuclei have
remained on one side of the septum after centrifugation. The three
nuclei may fuse in the following mitosis, which always occurs simultaneously in all three nuclei. The triploid cells are sometimes larger
than the diploid cell and hypertrophie features are prominent. No clone
has resulted ; the cells divide only once or, very rarely, twice.
B. Aneuploidy
If cells of Micrasterias rotata var. evoluta are centrifuged at metaphase,
in the same way that was used to obtain binucleate and enucleate cells,
it may happen that the nucleus becomes divided into more than two
daughter nuclei. This phenomenon has been called nuclear splitting
(Waris, 1958). In several cases three daughter nuclei have been obtained, one of the normal size and two smaller. In one particular case it
could be concluded that after centrifugation one of the two anaphase
groups had become severed by the new septum, giving rise to two
deficient nuclei. One of the daughter cells received a normal and a
deficient nucleus, the other only a deficient one. After fusion of the two
unequal nuclei, the former cell gave rise to a hyperhaploid clone which
since then has been in culture, while the latter cell with the deficient
nucleus remained alive for 1 month, exhibiting symptoms of increasing
morbidity, and died without dividing.
The hyperhaploid clone has certain features in common with the
diploid clones. Both may give rise to cells with lobes duplicated on two
levels and with adjacent gaps, but in the hyperhaploid cells, as a rule,
the lobe duplication does not involve more than about a half of the
lateral lobes, while in the diploid cells all of them may become duplicated. Although the lobe duplication is characteristic of both the diploid
and hyperhaploid clones, the majority of the cells may develop lobes
in one level. A difference appears in the size, which is in the diploid cells
larger, in the hyperhaploid cells rather smaller than in the normal
haploid cells. The hyperhaploid clone has not proved quite stable, for
some of the cells have eventually, after several years' culture, reverted
to the normal haploid form.
I X . The Effect of Ultraviolet Radiation
Ultraviolet radiation has many detrimental effects that vary with
the dose and the developmental phase of the cell at the time of exposure.
A standard lethal dose has been taken to be the dose which, when given
H. W A R I S A N D P. K A L L I O
cumulative effect of nuclear quantity on morphology is seen. The cell is,
however, almost always smaller in size than the diploid form.
Triploid cells are sometimes produced from binucleate complex cells
of type II (cf. Section VII) when three of the four daughter nuclei have
remained on one side of the septum after centrifugation. The three
nuclei may fuse in the following mitosis, which always occurs simultaneously in all three nuclei. The triploid cells are sometimes larger
than the diploid cell and hypertrophie features are prominent. No clone
has resulted ; the cells divide only once or, very rarely, twice.
B. Aneuploidy
If cells of Micrasterias rotata var. evoluta are centrifuged at metaphase,
in the same way that was used to obtain binucleate and enucleate cells,
it may happen that the nucleus becomes divided into more than two
daughter nuclei. This phenomenon has been called nuclear splitting
(Waris, 1958). In several cases three daughter nuclei have been obtained, one of the normal size and two smaller. In one particular case it
could be concluded that after centrifugation one of the two anaphase
groups had become severed by the new septum, giving rise to two
deficient nuclei. One of the daughter cells received a normal and a
deficient nucleus, the other only a deficient one. After fusion of the two
unequal nuclei, the former cell gave rise to a hyperhaploid clone which
since then has been in culture, while the latter cell with the deficient
nucleus remained alive for 1 month, exhibiting symptoms of increasing
morbidity, and died without dividing.
The hyperhaploid clone has certain features in common with the
diploid clones. Both may give rise to cells with lobes duplicated on two
levels and with adjacent gaps, but in the hyperhaploid cells, as a rule,
the lobe duplication does not involve more than about a half of the
lateral lobes, while in the diploid cells all of them may become duplicated. Although the lobe duplication is characteristic of both the diploid
and hyperhaploid clones, the majority of the cells may develop lobes
in one level. A difference appears in the size, which is in the diploid cells
larger, in the hyperhaploid cells rather smaller than in the normal
haploid cells. The hyperhaploid clone has not proved quite stable, for
some of the cells have eventually, after several years' culture, reverted
to the normal haploid form.
I X . The Effect of Ultraviolet Radiation
Ultraviolet radiation has many detrimental effects that vary with
the dose and the developmental phase of the cell at the time of exposure.
A standard lethal dose has been taken to be the dose which, when given