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PACIFIC SCIENCE, Vol. IV, April, 1950 
Fig. 10. Acrothamnion pulchellum J. A g. : a, part of the lower portion of a frond, showing two 
pairs of pinnae transversales developing on the same side of the axis, and a rhizoidal filament aris- 
ing from the lowest cell of a pinna; b, the same, showing rhizoidal filaments; c, the branching at the 
distal end of two rhizoidal filaments; d, apical portion of a short branch; e, very young branch devel- 
oping from the lowest cell of a principal pinna; f, initial of a branch developing from the lowest cell 
of an upper principal pinna, a and b, X 150; c, d, e, and f, X 245. 
erally simple, with tapering but not acute 
tips. Rarely some of them on a principal 
pinna are crowned with two opposite ramuli 
supporting an apical gland cell at their fork, 
in just the same manner as in the apex of a 
pinna. In the lower portion of the frond, the 
structure of pinnae is apt to become irreg- 
ular; in other words, pinnulae often dis- 
appear partly or entirely from principal 
pinnae or accessory pinnae, respectively. An 
accessory pinna which thus remains entirely 
simple is no longer crowned with a gland 
cell. The gland cell rests solitarily at the 
apex of each pinna, always on five cells cov- 
ering the uppermost axial cell of the pinna 
and two lowermost cells of each pinnula aris- 
ing oppositely from the uppermost axial cell 
of the pinna. The principal pinnae or lateral 
