586 Church . — The Structure of the T halites of 
presents no peculiarity beyond a further increase in the length 
of its segments. Only the upper whorls of the plant possess 
undamaged appendages ; those further back retain for a con- 
siderable period the short basal portions of Stage II, but 
present few traces if any of Stage I. The base of the main 
axis is now becoming considerably thickened by internal 
apposition of layers ; wear and tear of the outermost layers 
which alone were perforated at the older scars, together with 
alterations in volume of the main tube, soon lead to oblitera- 
tion of the first-formed scars, and in this and further stages, 
as a rule, no traces of earlier formations remain. 
This second type of lateral appendage also obtains for 
many nodes ; thus, 4 specimens averaging 16 mm. in length, 
and showing traces of Type I attached to a lower whorl of 
scars, while the apex was passing on to Stage III, gave 
evidences of the second type of formation on 28-46 nodes ; 
the average being 37. Again, 11 specimens, 10-19 mm. in 
length, in which the apical whorls were passing on to Stage III, 
but in which no trace of Stage I remained, showed relics of 
basal segments of the second type on 28-84 nodes. Thus, 
an average plant, 15*5 mm. in length, would have laid down 
50 whorls of appendages of the form characteristic of Stage II. 
Stage III. 
The short basal portions, formed, as shown, by abstriction 
from the elongated basal segments of Stage I, remain fairly 
constant for Stage II (Fig. 11) ; but, in later-formed whorls, 
they exhibit a tendency to dilate, especially on the acroscopic 
surface (Fig. 12), and thus soon come into lateral contact with 
their neighbours. This dilatation may increase by degrees 
over several internodes, or may be so hastened that the 
transition is complete in passing from one whorl to the next ; 
the ultimate result being the formation of a ‘ cortex ’ of 
bladder-like basal segments, completely hiding the main 
axis, and appearing externally as a facetted layer, of which 
the component units are pressed into close lateral contact, 
