52
H. WARIS AND P. KALLIO
A. Uniradiate Cells
Uniradiate cells have been obtained from five species, namely M.
thomasiana var. notata, M. rotata var. evoluta, M. torreyi, M. americana
and M.fimbriata (Fig. 2).
The first case was established in M. thomasiana var. notata. In a clone
culture of this species there appeared spontaneously a defective form
lacking the lateral lobes of one side (Waris, 1950b). From such a cell a
clone was derived which after about ten years' culture still showed a
majority of defective cells, though some of the offspring had reverted to
the normal form. The cells which had reassumed the normal form gave
rise to normal offspring. Cultures of the defective form have been maintained until now, but unless the cultures are renewed by repeated
transfer of defective cells to new nutrient solutions the majority of the
cells eventually come to be normal owing to the lower viability of the
defective cells. The latter are extremely sensitive to unfavourable conditions, a fact which is manifested in the great variability of the forms
in old cultures (Waris, 1950b ; Kallio, 1951). In fact, the term 'uniradiate'
does not express the whole truth concerning the form ; for instance, a
duplication of the lobes or their parts on two levels, accompanied by the
formation of gaps adjacent to the duplicated parts, frequently occurs.
At the same time there appear cells indicating a transition to the
normal type.
The manner in which the first defective cell originated was not
noticed, but Kallio (1951) had an opportunity to observe new cases
which have been described in detail. One of the cases was rather complicated; a cell exposed to cold shock at telophase gave rise to two
daughter cells, one of which divided normally while the other was a
complex cell with two isthmuses and two haploid nuclei ; the complex
cell produced two uniradiate cells. Another case was simpler: in a
culture a cell was found which consisted of a normal and a uniradiate
semicell ; in the next division the latter semicell formed a new one of the
same type and thus gave rise tp a uniradiate cell. It seems that this
simpler case also corresponds to the origination of the uniradiate forms
in other species, such as M. rotata var. evoluta (Kallio, 1954).
The reversion of the uniradiate M. thomasiana var. notata to the
normal form has been described in detail by Kallio (1951). It usually
takes place by one of the two unilateral parent semicells forming a new
bilateral semicell with the two wings at an acute angle. In subsequent
cell divisions new semicells will be formed in which the two lobed wings
approach the same level until the normal form is achieved.
The origination of the uniradiate form was called 'mutation' (Waris,
1950b) and its reversion to the normal type 'remutation', meaning that
H. WARIS AND P. KALLIO
A. Uniradiate Cells
Uniradiate cells have been obtained from five species, namely M.
thomasiana var. notata, M. rotata var. evoluta, M. torreyi, M. americana
and M.fimbriata (Fig. 2).
The first case was established in M. thomasiana var. notata. In a clone
culture of this species there appeared spontaneously a defective form
lacking the lateral lobes of one side (Waris, 1950b). From such a cell a
clone was derived which after about ten years' culture still showed a
majority of defective cells, though some of the offspring had reverted to
the normal form. The cells which had reassumed the normal form gave
rise to normal offspring. Cultures of the defective form have been maintained until now, but unless the cultures are renewed by repeated
transfer of defective cells to new nutrient solutions the majority of the
cells eventually come to be normal owing to the lower viability of the
defective cells. The latter are extremely sensitive to unfavourable conditions, a fact which is manifested in the great variability of the forms
in old cultures (Waris, 1950b ; Kallio, 1951). In fact, the term 'uniradiate'
does not express the whole truth concerning the form ; for instance, a
duplication of the lobes or their parts on two levels, accompanied by the
formation of gaps adjacent to the duplicated parts, frequently occurs.
At the same time there appear cells indicating a transition to the
normal type.
The manner in which the first defective cell originated was not
noticed, but Kallio (1951) had an opportunity to observe new cases
which have been described in detail. One of the cases was rather complicated; a cell exposed to cold shock at telophase gave rise to two
daughter cells, one of which divided normally while the other was a
complex cell with two isthmuses and two haploid nuclei ; the complex
cell produced two uniradiate cells. Another case was simpler: in a
culture a cell was found which consisted of a normal and a uniradiate
semicell ; in the next division the latter semicell formed a new one of the
same type and thus gave rise tp a uniradiate cell. It seems that this
simpler case also corresponds to the origination of the uniradiate forms
in other species, such as M. rotata var. evoluta (Kallio, 1954).
The reversion of the uniradiate M. thomasiana var. notata to the
normal form has been described in detail by Kallio (1951). It usually
takes place by one of the two unilateral parent semicells forming a new
bilateral semicell with the two wings at an acute angle. In subsequent
cell divisions new semicells will be formed in which the two lobed wings
approach the same level until the normal form is achieved.
The origination of the uniradiate form was called 'mutation' (Waris,
1950b) and its reversion to the normal type 'remutation', meaning that