590 Church . — The Structure of the Thallus of 
to 100-200, but varies considerably in different specimens. 
The apex does not calcify, the first trace of deposit being 
found at about the tenth node from the growing-point. The 
whole of the surfaces bounding the cavities beneath the 
cortical layer are incrusted, the maximum deposit forming 
a layer beneath the dilated ends of the cortical segments, 
perforated only by the pedicel portions. The deposit appears 
as an extremely fine precipitate of calcium carbonate in 
a mucilaginous outer layer of the cell-membrane (Fig. 21), 
but further details may be left for consideration in connexion 
with the calcification of the mature thallus. 
Stage V. 
As already shown, the plant vegetates for a considerable 
period in Stage IV, increasing steadily in length, diameter of 
the main axis, and number of appendages in a single whorl 
(Figs. 28, 29) ; these last being 30-32 in the mature plant. 
The new epoch is inaugurated by the appearance of the 
reproductive organs as new and special formations. These 
arise as outgrowths of the basal segments in the angle of the 
first dichotomy of the appendage, that is to say, in the 
angle between the cortical segments (Figs. 32, 33). Appear- 
ing first at the 6th node from the apex in the form of 
a papilla-like projection at the extreme distal end of the 
basal segments, they soon develop into spherical stalked 
structures, and are delimited from the rest of the lateral 
member by the characteristic ring-septum. They possess 
abundant protoplasmic contents and chlorophyll, and rapidly 
calcify. At about the 60th node from the apex they are 
plugged off by a cellulose stopper (Fig. 31). The contents 
round off, and secrete a new cellulose membrane which fits 
closely the spherical terminal portion of the structure 1 
(Fig. 27). Although further development is unknown, there 
can be little doubt that we have here to deal with an aplano- 
sporangium containing a single aplanospore. The formation 
1 Cramer, loc. cit., p. 31 ; Solms, loc. cit., p. 64. 
