132
LUISE STANGE
while in the cells near the base division has ceased. Thus, a striking
contrast exists between the activity of cell division of prothallial cells
before isolation and their regenerative ability after isolation. Beside this
apico-basal gradient in the ability to regenerate, another gradient in the
abilities of cell elongation and proliferation of the regenerates was
demonstrated. On the 5th day after the formation of the first protonema
cell, the length of each protonema was measured and the number of
cells counted (Fig. 5b). When the cells were isolated from the basal part
of the prothallium, the regenerative protonema was longer and the
number of cells was smaller in comparison with the length and cell
number in regenerates of the apical part. Thus, in regenerates from cells
of the more basal region of the prothallium, elongation predominated
over proliferation and vice versa in those of the more apical region.
In interpreting the results, Ito (1962) states at first that all cells of
young gametophytes of Pteris vittata, except the rhizoids, 'retain a
totipotency, in other words, to a certain degree an embryonality or a
spore-nature'. (By the term 'spore-nature' the author refers to the
fact that the growth of a sporeling immediately after germination is
exclusively based on substances stored in the spore. The importance of
these substances for growth decreases gradually and the growth of the
sporeling becomes more and more supported by substances synthesized
by the new cells themselves.) This 'spore-nature' of the cells decreases
with increasing age, and with displacement toward the base. The author
assumes that each cell of the meristematic region, by itself, has only a
low activity of cell division. The actual high activity of division in
meristematic cells results from the connexions with cells of the other
part of the plant, presumably by provision of substances or by some
stimulation from the older cells. The observation of Albaum (1938a)
that the activity of cell division in the meristematic region of a gametophyte decreased markedly after its isolation from the basal part supports this view.
I t would be very desirable to extend these interesting observations to
still earlier events in the regeneration process, namely to the first
nuclear division in the isolated cell and to the preceding changes.
Relative to these processes indicating the critical shift in cell behaviour,
the formation of the rhizoid and the first protonema cell are late processes. For the formation of the rhizoid, the cell must already be able to
elongate. It is known that in regenerating cells several nuclear and cell
divisions can precede the onset of elongation, thus leading to several
very small cells inside the mother cell (e.g. Isaburo-Nagai, 1914;
Linsbauer, 1926; Stange, 1957). On the other hand, in Riella there is
some evidence that the rhizoid has an important function in cell proliferation (Stange, unpublished result). After cutting off the rhizoids
LUISE STANGE
while in the cells near the base division has ceased. Thus, a striking
contrast exists between the activity of cell division of prothallial cells
before isolation and their regenerative ability after isolation. Beside this
apico-basal gradient in the ability to regenerate, another gradient in the
abilities of cell elongation and proliferation of the regenerates was
demonstrated. On the 5th day after the formation of the first protonema
cell, the length of each protonema was measured and the number of
cells counted (Fig. 5b). When the cells were isolated from the basal part
of the prothallium, the regenerative protonema was longer and the
number of cells was smaller in comparison with the length and cell
number in regenerates of the apical part. Thus, in regenerates from cells
of the more basal region of the prothallium, elongation predominated
over proliferation and vice versa in those of the more apical region.
In interpreting the results, Ito (1962) states at first that all cells of
young gametophytes of Pteris vittata, except the rhizoids, 'retain a
totipotency, in other words, to a certain degree an embryonality or a
spore-nature'. (By the term 'spore-nature' the author refers to the
fact that the growth of a sporeling immediately after germination is
exclusively based on substances stored in the spore. The importance of
these substances for growth decreases gradually and the growth of the
sporeling becomes more and more supported by substances synthesized
by the new cells themselves.) This 'spore-nature' of the cells decreases
with increasing age, and with displacement toward the base. The author
assumes that each cell of the meristematic region, by itself, has only a
low activity of cell division. The actual high activity of division in
meristematic cells results from the connexions with cells of the other
part of the plant, presumably by provision of substances or by some
stimulation from the older cells. The observation of Albaum (1938a)
that the activity of cell division in the meristematic region of a gametophyte decreased markedly after its isolation from the basal part supports this view.
I t would be very desirable to extend these interesting observations to
still earlier events in the regeneration process, namely to the first
nuclear division in the isolated cell and to the preceding changes.
Relative to these processes indicating the critical shift in cell behaviour,
the formation of the rhizoid and the first protonema cell are late processes. For the formation of the rhizoid, the cell must already be able to
elongate. It is known that in regenerating cells several nuclear and cell
divisions can precede the onset of elongation, thus leading to several
very small cells inside the mother cell (e.g. Isaburo-Nagai, 1914;
Linsbauer, 1926; Stange, 1957). On the other hand, in Riella there is
some evidence that the rhizoid has an important function in cell proliferation (Stange, unpublished result). After cutting off the rhizoids