MORPHOGENESIS IN
MICRASTERIAS
65
The continuity and the reproduction of the plasmatic skeleton is
supposed to be controlled by the nuclear effect during the metabolic
phase of the developmental cycle of the cell (cf. Kallio, 1959). Whereas
the normal (constant) cell form is dependent on the synchronous division (duplication) of various structural units, this synchronism is disturbed in these cases. When two equal plasmatic units compete for the
same nuclear effect controlling their development, the development of
one of them may be retarded, so that at the moment when cytokinesis
begins, this unit is too immature to duplicate. I t may, however, divide
at the next division, which means that its developmental cycle has
doubled in length.
VIII. Changes in the Chromosome Complement
A. Polyploidy
A polyploid cell is understood in this paper to mean a cell in which the
chromosome number of the nucleus is a multiple of the number in the
species as found in nature without taking any stand as to the origin of
the chromosome number of the species.
Polyploid forms of the following Micrasterias species have been
artificially produced by various methods : M. thomasiana, M. thomasiana
var. notata, M. rotata, M. rotata var. evoluta, M. angulosa, M. denticulata,
M. torreyi, M. fimbriata, M. radiata, M. ceratophora, M. papillifera,
M. sol, M. americana. Other desmids in which ploidization has been
effected are PUurotaenium trdbecula, P. miniatum and Closterium
malinvernianum,
although no permanent polyploid clones of these
species have resulted.
Diploid nuclei have arisen in most cases from the fusion of the two
adjoining nuclei in binucleate cells of the type I I described in Section
VII. Tetraploid nuclei have been produced by the same methods from
diploid nuclei, and triploid nuclei from three haploid nuclei.
Only rarely do diploid nuclei result from a disturbance in the division
of a nucleus after the chromosomes have doubled. This has, however,
occurred in plasmolysis experiments, cold treatments (Kallio, 1951),
and experiments in which haploid cells in metaphase were transferred
to Waris' (1953) MS-solution containing 10
- 3
mole of sodium 2,
4-dinitrophenolate per 1 for a period of 4 h (Kallio and Karunen, unpublished).
The characteristic features of biradiate diploids are the same in
principle in different Micrasterias species. There are, however, two
different types of diploid cells, one with a biradiate or two-winged
faciès and one with more than two wings. The diploid cells are larger
than the haploids in all Micrasterias species studied. The mean ratio of
MICRASTERIAS
65
The continuity and the reproduction of the plasmatic skeleton is
supposed to be controlled by the nuclear effect during the metabolic
phase of the developmental cycle of the cell (cf. Kallio, 1959). Whereas
the normal (constant) cell form is dependent on the synchronous division (duplication) of various structural units, this synchronism is disturbed in these cases. When two equal plasmatic units compete for the
same nuclear effect controlling their development, the development of
one of them may be retarded, so that at the moment when cytokinesis
begins, this unit is too immature to duplicate. I t may, however, divide
at the next division, which means that its developmental cycle has
doubled in length.
VIII. Changes in the Chromosome Complement
A. Polyploidy
A polyploid cell is understood in this paper to mean a cell in which the
chromosome number of the nucleus is a multiple of the number in the
species as found in nature without taking any stand as to the origin of
the chromosome number of the species.
Polyploid forms of the following Micrasterias species have been
artificially produced by various methods : M. thomasiana, M. thomasiana
var. notata, M. rotata, M. rotata var. evoluta, M. angulosa, M. denticulata,
M. torreyi, M. fimbriata, M. radiata, M. ceratophora, M. papillifera,
M. sol, M. americana. Other desmids in which ploidization has been
effected are PUurotaenium trdbecula, P. miniatum and Closterium
malinvernianum,
although no permanent polyploid clones of these
species have resulted.
Diploid nuclei have arisen in most cases from the fusion of the two
adjoining nuclei in binucleate cells of the type I I described in Section
VII. Tetraploid nuclei have been produced by the same methods from
diploid nuclei, and triploid nuclei from three haploid nuclei.
Only rarely do diploid nuclei result from a disturbance in the division
of a nucleus after the chromosomes have doubled. This has, however,
occurred in plasmolysis experiments, cold treatments (Kallio, 1951),
and experiments in which haploid cells in metaphase were transferred
to Waris' (1953) MS-solution containing 10
- 3
mole of sodium 2,
4-dinitrophenolate per 1 for a period of 4 h (Kallio and Karunen, unpublished).
The characteristic features of biradiate diploids are the same in
principle in different Micrasterias species. There are, however, two
different types of diploid cells, one with a biradiate or two-winged
faciès and one with more than two wings. The diploid cells are larger
than the haploids in all Micrasterias species studied. The mean ratio of