MORPHOGENESIS IN
MICRASTERIAS
67
haploids. Thus, for example, a temperature of 25° C kills a M. thomasiana
diploid, but not a haploid clone.
Diploids with a greater number of wings also exist in Micrasterias.
When M. thomasiana is ploidized, all side lobes usually form sublobes
at two different levels. A variation in cell morphology is particularly
prominent. After several cell divisions, however, a new type of cell is
formed 'spontaneously'. Whereas the normal haploid as well as the
diploid described above are biradiate, these are triradiate or threewinged. There is one polar lobe, but three side lobe complexes or wings
forming an angle of 120° with one another. The size of the cell is about
twice as large and the sinus angle somewhat larger than in the haploid.
Doubling of the secondary lobes is rarely seen. The division rate of the
triradiate faciès is higher than that of the biradiate diploid.
Similar diploids have been produced from M. rotata var. evoluta
(Kallio, 1954), M. angulosa, and M. torreyi. Each of these species have
formed a permanent triradiate clone. These clones never or only rarely
remutate into the biradiate faciès. This has been observed only once in
M. torreyi.
A four-winged (quadriradiate) faciès has been produced from M.
thomasiana. The wings in these diploid cells are similar in form and size
to those in normal haploid cells.
The characteristics of the different types of diploid cells reflect the
significance of the relationship of nuclear quantity to the protoplasmic
unit. As the nuclear quantity per wing in the biradiate diploid is twice
that in the haploid, the size as well as the morphological complexity
increase and the tendency to lobe doubling is strong. The supra-optimal
nuclear effect per wing is seen in the morphology. These changes are not
so prominent in the wings of triradiate diploids and in the quadriradiate
faciès with an unchanged nuclear-cytoplasmic ratio, in the individual
wings of which no differences in form are noted when compared with the
biradiate haploid wings.
Ploidization of the uniradiate (haploid) cell always leads to the formation of the normal two-winged haploid form in M. thomasiana var.
notata. The haploid form of this species exists in two faciès, the uniradiate
and biradiate, but the uniradiate does not exist at the diploid level.
From M. thomasiana (type form) bi-, tri- and quadriradiate diploids
have been obtained, the triradiate being the most frequent one.
Only bi- and triradiate facies of M. angulosa and M. torreyi diploid
forms exist. The nucleus evidently controls the limits of variation in this
respect.
Tetraploid cells can often be produced from diploids in the same
manner as the latter from haploids. The viability of tetraploids is low
and no permanent constant clones have resulted. In some cases a
MICRASTERIAS
67
haploids. Thus, for example, a temperature of 25° C kills a M. thomasiana
diploid, but not a haploid clone.
Diploids with a greater number of wings also exist in Micrasterias.
When M. thomasiana is ploidized, all side lobes usually form sublobes
at two different levels. A variation in cell morphology is particularly
prominent. After several cell divisions, however, a new type of cell is
formed 'spontaneously'. Whereas the normal haploid as well as the
diploid described above are biradiate, these are triradiate or threewinged. There is one polar lobe, but three side lobe complexes or wings
forming an angle of 120° with one another. The size of the cell is about
twice as large and the sinus angle somewhat larger than in the haploid.
Doubling of the secondary lobes is rarely seen. The division rate of the
triradiate faciès is higher than that of the biradiate diploid.
Similar diploids have been produced from M. rotata var. evoluta
(Kallio, 1954), M. angulosa, and M. torreyi. Each of these species have
formed a permanent triradiate clone. These clones never or only rarely
remutate into the biradiate faciès. This has been observed only once in
M. torreyi.
A four-winged (quadriradiate) faciès has been produced from M.
thomasiana. The wings in these diploid cells are similar in form and size
to those in normal haploid cells.
The characteristics of the different types of diploid cells reflect the
significance of the relationship of nuclear quantity to the protoplasmic
unit. As the nuclear quantity per wing in the biradiate diploid is twice
that in the haploid, the size as well as the morphological complexity
increase and the tendency to lobe doubling is strong. The supra-optimal
nuclear effect per wing is seen in the morphology. These changes are not
so prominent in the wings of triradiate diploids and in the quadriradiate
faciès with an unchanged nuclear-cytoplasmic ratio, in the individual
wings of which no differences in form are noted when compared with the
biradiate haploid wings.
Ploidization of the uniradiate (haploid) cell always leads to the formation of the normal two-winged haploid form in M. thomasiana var.
notata. The haploid form of this species exists in two faciès, the uniradiate
and biradiate, but the uniradiate does not exist at the diploid level.
From M. thomasiana (type form) bi-, tri- and quadriradiate diploids
have been obtained, the triradiate being the most frequent one.
Only bi- and triradiate facies of M. angulosa and M. torreyi diploid
forms exist. The nucleus evidently controls the limits of variation in this
respect.
Tetraploid cells can often be produced from diploids in the same
manner as the latter from haploids. The viability of tetraploids is low
and no permanent constant clones have resulted. In some cases a