The Old IVood and the New. 
O *7 
2 / 
tracheides of the central mass are extremely short, and ill-adapted 
for conduction. The old central wood, finding itself relieved of 
its original duty by the new secondary tissues, has, as it were, taken 
the alarm, and hy adapting itself to a new function—that of water- 
storage— is able, for a time, to maintain its existence. 
Lyginodendron (Lower Carboniferous and Coal-measures). 
Here the central wood has disappeared altogether, and is replaced 
by pith; from this stage onwards, leaf-traces and secondary wood 
are alone represented. The structure of the leaf-trace strands 
themselves, however, is precisely the same as in Heterangium. 
Everything supplementary to them is henceforth supplied by the 
secondary wood alone. Lyginodendron is the typical stem for 
complete persistence of the centripetal wood in the leaf-trace 
system, while it has disappeared elsewhere. The bundles of the 
stew have here a structure identical with that of the /^/-bundles in 
Cycads. In the leaf of Lyginodendron the bundles were still 
concentric, and therefore Fern like, as was the general habit. 
Cidmnopitys 1 (Lower Carboniferous). In C. fascicularis the 
grade of structure is almost like that of Lyginodendron. The leaf- 
trace strands are largest where they leave the pith, and are here 
typically mesarch, with well-developed centripetal wood; traced 
downwards from this point the latter becomes much reduced, but 
does not wholly disappear. C. beinertianum goes a step further. 
Here the leaf-traces only have centripetal xylem where they approach 
their exit ; lower down in the stem they lose it altogether, so that 
in most of the strands around the pith the structure is purely 
endarch. This stem thus marks an important step towards the 
characteristic Gymnospermous anatomy. Calaniopitys, judging 
from the German species, C. Saturni, was probably still Fern-like 
in habit. 
Pitys (Lower Carboniferous). This genus diverges a little from 
our series; it no doubt approached the Gymnosperms nearly, and 
was perhaps itself an early representative of the Cordaiteae 2 . The 
structure is remarkable; in P. antiquci (Witham’s “Lennel Braes 
Tree”) a great number (40-50) of mesarch xylem-strands surround 
the large pith, but they are very small, and most Qf them are 
embedded in the tissue of the pith, and thus isolated from the rest 
most inappropriate name, maintained in deference to the 
law of priority. There is no real affinity to Calamarieae. 
11 The great trunk in the garden of the Natural History Museum 
belongs to a species of Pitys. 
