THE DEVELOPMENT OF THE THALLUS OF SPHAEROCARPOS 
DONNELLH AUST. 
H, W. RiCKETT 
The Germination of the Spore 
Previous descriptions of the germination of the spore of Sphaerocarpos 
represent two conflicting views. One of these is held by Leitgeb and Goebel, 
the opposing one by Campbell. These are the only authors who have 
described spore germination in Sphaerocarpos. Leitgeb (9), the first to 
study this subject, identifies the method of spore - germination with that 
typical for the Ricciaceae and Marchantiaceae. There is, according to him, 
a germ tube formed, consisting at first of a single cell, and later of several 
tiers of cells arranged in groups of four. The terminal quadrant of this 
structure forms the germinal disc, and one of its cells becomes the apical 
cell of the thallus. The latter grows out in a plane at right angles to the 
long axis of the germ tube. The apical cell is at first two-sided, cutting off 
two sets of lateral segments; it is later replaced by a four-sided apical cell, 
forming dorsal and ventral segments in addition to the lateral ones, and 
thus causing the thickening of the thallus. The first rhizo'd is formed very 
early, but he states that its connection with the sporeling was to him obscure, 
though obviously arising from a previous division of the original cell. 
Campbell (3), studying spore germination in Riccia, was unable to 
confirm this account ; according to him growth is continuous in one direction 
throughout the history of the sporeling, and there is no format on of a 
germinal disc or plate on the end of, and at right angles to, the germ tube. 
According to his description, the germ tube, consisting of several tiers of 
cells, is formed as described by Leitgeb, and from one of the terminal cells a 
two-sided apical cell, later replaced by a four-sided cell, is formed; but 
growth resulting from the segmentation of this apical cell takes place in the 
same direction as does that of the germ tube. He agrees with Leitgeb in 
classifying Sphaerocarpos with the typical Ricciaceae and Ma.rchantiaceae 
so far as the method of spore germination is concerned, but differs from 
him in his description of the method by which this takes place. In his 
account of the process in Sphaerocarpos (2), he describes in detail the way 
in which the two-sided apical cell is replaced by a four-sided cell. The two- 
sided cell is divided by a basal (posterior) wall in a vertical transverse direc- 
tion, and then begins to cut off three sets of segments instead of two, two 
lateral and one basal. Later, two sets of basal segments are formed, the 
one basal wall being replaced by two inclined to one another. Thus finally 
four sets of segments are formed, two lateral, one dorsal-posterior, and one 
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