V. DETERMINING
FACTORS IN CELL
GROWTH
223
space within the old wall, (i.e. they tend to be tetrakaidecahedra) but
they will depart from this shape in accordance with any asymmetry in
the confining space they are to fill (see Steward, 1939; plate 7, Figs. A-C).
However, these same sporelings may grow in an entirely different
way if they are freed from this restriction and are asymmetrically
FIG. 3. Growth Forms in Free Cells and Clusters, (a) Germinating aplanospore of
Valonia ventricosa {after Steward, 1939). (6, c) Morulloid stages in the growth of spore -
lings of V. ocellata within old vesicle (after Steward, 1939). (d) Sporelings of V. ocellata
with filaments growing horizontally and away from light (after Steward, 1939). (e) Enlarged cell from banana pulp callus.
stimulated. Under the influence of unilateral light using a source rich in
the red, the spherical cells grow at their tips and produce a filamentous
outgrowth away from the light (Fig. 3(d)). Electron microscopy shows
that the first formed cellulose wall of the spherical sporelings is a