Unipolar spore germination in Aloina gives rise to wide (20-24 mu m di
ameter) protonemal axes with oblique cross-walls and spindle-shaped ch
loroplasts. The original protonemal filaments are caulonemal but they
produce narrower (9-12 mu m diameter) chloronemal side branches, with
ovoid to spherical chroroplasts in shortly cylindrical cells which hav
e transverse cross-walls. The mature protonema comprises only four to
six widely spreading major caulonemal axes with occasional gametophore
s, a pattern of morphogenesis that explains the scattered gametophores
of Aloina in nature. After prolonged culture the older chloronemal fi
laments become;highly attenuated whereas wall thickening occurs in the
caulonemal axes and younger chloronemata are transformed into chains
of thick-walled brood cells containing large quantities of lipid. This
phenomenon, hastened by abscisic acid and drying out of the cultures,
is also found in nature. On Parker nutrient medium the filament syste
ms produced from gametophores and isolated leaves are identical to pro
tonemata. In the absence of nutrients the side branches of all the fil
ament systems are very narrow (3-5 mu m diameter) and closely similar
to those found in nature. The filaments produced by Aloina never have
pigmented walls. The protonemal brood cells are closely similar to lea
f lamellar cells; both are naturally occurring thick-walled vegetative
diaspores, which germinate into protonemata after long periods of des
iccation.