118
LUISE STANGE
regeneration of various mosses and liverworts, Heitz (1925) was the first
to note the cytological changes preceding the first cell division. The
liverworts Lophocolea and Pellia proved to be specially suitable for these
observations, but other liverworts and mosses showed comparable
results. When the unistratose leaves of Lophocolea were isolated, the
most striking changes in the cells were observed after about 6-8 days.
In several cells the chloroplasts, which are normally distributed along
the cell walls, became conglomerated in the centres of the cells (cf. Fig.
2). However, this displacement of the chloroplasts was not the first and
only change in the cells occurring after isolation of the leaf. After some
days of isolation the nuclei of several cells also moved from their regular
position at a cell wall perpendicular to the leaf plane to a more central
position. At the same time the nuclei and nucleoli increased considerably
in size. This movement and increase in size of the nucleus was one of the
first observable changes in the cells of the isolated leaf. Previously some
protoplasmic filaments had been formed across the cell. Nucleus and
chloroplasts migrated along these filaments to the centre of the cell.
The chloroplasts divided and decreased in size during this time (cf.
Correns, 1899; Heitz, 1922). These changes are believed to reconstitute
conditions similar to those in meristematic cells. The cluster of chloroplasts was then divided into two halves and the chloroplasts were distributed to the two poles of the mitotic division apparatus. An increase in
nuclear and nucleolar size was not only observed in the cells entering
division but, after 8 days, also in other non-dividing cells of the isolated
leaves, although to a lesser extent. Division of chloroplasts also occurred
in non-dividing cells (Heitz, 1922).
These results were confirmed and extended in more recent investigations on regeneration in the liverwort Riella helicophylla (Stange, 1954,
1957). This liverwort shows a relatively simple organization (cf. Fig. 6).
The adult thallus consists of a multicellular rib or axis and a broad
unistratose wing. The meristem is situated at the apex of the plant.
Therefore, proceeding in the wing from the apex to the base, cells of
increasing age are found. Rhizoids are present at the base of the rib.
By cutting fragments out of the wing, regeneration is easily induced in
the cells of the isolated tissue. One of the first signs of embryonization
in these cells is a considerable increase in the size of the nucleolus which
is very small in mature cells. At the same time the stainability of the
nucleolus by basic dyes increases. After treatment with ribonuclease
this stainability was almost completely removed. Therefore, the increase in nucleolar size must be accompanied by a synthesis of ribonucleic acid (RNA). After application of the cytochemical arginine
reaction (Serra, 1944) the nucleoli gave a positive result, the intensity
of which was higher in the large nucleoli of the regenerating cells. Thus,
LUISE STANGE
regeneration of various mosses and liverworts, Heitz (1925) was the first
to note the cytological changes preceding the first cell division. The
liverworts Lophocolea and Pellia proved to be specially suitable for these
observations, but other liverworts and mosses showed comparable
results. When the unistratose leaves of Lophocolea were isolated, the
most striking changes in the cells were observed after about 6-8 days.
In several cells the chloroplasts, which are normally distributed along
the cell walls, became conglomerated in the centres of the cells (cf. Fig.
2). However, this displacement of the chloroplasts was not the first and
only change in the cells occurring after isolation of the leaf. After some
days of isolation the nuclei of several cells also moved from their regular
position at a cell wall perpendicular to the leaf plane to a more central
position. At the same time the nuclei and nucleoli increased considerably
in size. This movement and increase in size of the nucleus was one of the
first observable changes in the cells of the isolated leaf. Previously some
protoplasmic filaments had been formed across the cell. Nucleus and
chloroplasts migrated along these filaments to the centre of the cell.
The chloroplasts divided and decreased in size during this time (cf.
Correns, 1899; Heitz, 1922). These changes are believed to reconstitute
conditions similar to those in meristematic cells. The cluster of chloroplasts was then divided into two halves and the chloroplasts were distributed to the two poles of the mitotic division apparatus. An increase in
nuclear and nucleolar size was not only observed in the cells entering
division but, after 8 days, also in other non-dividing cells of the isolated
leaves, although to a lesser extent. Division of chloroplasts also occurred
in non-dividing cells (Heitz, 1922).
These results were confirmed and extended in more recent investigations on regeneration in the liverwort Riella helicophylla (Stange, 1954,
1957). This liverwort shows a relatively simple organization (cf. Fig. 6).
The adult thallus consists of a multicellular rib or axis and a broad
unistratose wing. The meristem is situated at the apex of the plant.
Therefore, proceeding in the wing from the apex to the base, cells of
increasing age are found. Rhizoids are present at the base of the rib.
By cutting fragments out of the wing, regeneration is easily induced in
the cells of the isolated tissue. One of the first signs of embryonization
in these cells is a considerable increase in the size of the nucleolus which
is very small in mature cells. At the same time the stainability of the
nucleolus by basic dyes increases. After treatment with ribonuclease
this stainability was almost completely removed. Therefore, the increase in nucleolar size must be accompanied by a synthesis of ribonucleic acid (RNA). After application of the cytochemical arginine
reaction (Serra, 1944) the nucleoli gave a positive result, the intensity
of which was higher in the large nucleoli of the regenerating cells. Thus,