122
LUISE STANGE
zahn (1960) followed the behaviour of the chloroplasts in cells of isolated
leaves during the process of embryonization. The size and number of
chloroplasts were determined in three different systems : (a) in isolated
half leaves; (b) in half leaves attached to a stem segment, and (c) in
whole leaves attached to a stem segment. In the first system a regenerative protonema is formed from the cells of isolated leaves, while in the
other two systems a protonema grows out only from stem cells (cf.
Section I I I , B). The determinations were carried out at increasing time
intervals after the preparation of the three systems and leaves from the
TIME
IN HOURS
TIME
IN
HOURS
O - O ISOL HALF A
° - ° ATT HALF A
A—A ATT WHOLE
A
0 - - 0 ISOL HALF B
° " ° ATT HALF B
Δ - - Δ ATT WHOLE
B
FIG. 3. Splachnum ampullaceum. Changes in chloroplast size and ehloroplast number
in cells of apical (A) and basal (B) leaves. Leaves were undivided (whole) or subdivided
into halves (half), isolated (isol) or attached (att) to a stem segment. The number of
chloroplasts per cell was determined for each point of the curves in an average of 30-40
cells with no more than four cells per leaf. Each number for chloroplast size represents an
average from 150 chloroplasts. (Redrawn from MacNutt and von Maltzahn, 1960.)
apex and from the base were compared (cf. Section I I I , A, 2). The results
(Fig. 3) indicate that in detached half leaves the number of chloroplasts
per cell increases and the size of chloroplasts decreases at the same time.
The attached half and attached whole leaves did not show any comparable changes. In cells of detached half leaves many dumb-bellshaped chloroplasts were observed, further demonstrating the divisional
activity of chloroplasts in these cells. Beside the dumb-bell-shaped
chloroplasts, which represent stages of fission into two differentiated
daughter chloroplasts of equal size, under the same experimental conditions an additional type of division was described in an investigation
LUISE STANGE
zahn (1960) followed the behaviour of the chloroplasts in cells of isolated
leaves during the process of embryonization. The size and number of
chloroplasts were determined in three different systems : (a) in isolated
half leaves; (b) in half leaves attached to a stem segment, and (c) in
whole leaves attached to a stem segment. In the first system a regenerative protonema is formed from the cells of isolated leaves, while in the
other two systems a protonema grows out only from stem cells (cf.
Section I I I , B). The determinations were carried out at increasing time
intervals after the preparation of the three systems and leaves from the
TIME
IN HOURS
TIME
IN
HOURS
O - O ISOL HALF A
° - ° ATT HALF A
A—A ATT WHOLE
A
0 - - 0 ISOL HALF B
° " ° ATT HALF B
Δ - - Δ ATT WHOLE
B
FIG. 3. Splachnum ampullaceum. Changes in chloroplast size and ehloroplast number
in cells of apical (A) and basal (B) leaves. Leaves were undivided (whole) or subdivided
into halves (half), isolated (isol) or attached (att) to a stem segment. The number of
chloroplasts per cell was determined for each point of the curves in an average of 30-40
cells with no more than four cells per leaf. Each number for chloroplast size represents an
average from 150 chloroplasts. (Redrawn from MacNutt and von Maltzahn, 1960.)
apex and from the base were compared (cf. Section I I I , A, 2). The results
(Fig. 3) indicate that in detached half leaves the number of chloroplasts
per cell increases and the size of chloroplasts decreases at the same time.
The attached half and attached whole leaves did not show any comparable changes. In cells of detached half leaves many dumb-bellshaped chloroplasts were observed, further demonstrating the divisional
activity of chloroplasts in these cells. Beside the dumb-bell-shaped
chloroplasts, which represent stages of fission into two differentiated
daughter chloroplasts of equal size, under the same experimental conditions an additional type of division was described in an investigation