Worsdell . — The Structure and Origin of the Cycadaceae. 14 1 
Lyginodendron . In the case of Lyginodendron , the near allies of the plant, 
viz. Cycadoxylon 1 and Medulloseae, exhibit this e anomaly ’ as the normal 
structure in their stem. Hence, the comparative method of investigation 
strongly supports my hypothesis that this so-called ‘ anomaly ’ in Lygino- 
dendron is a reversion to an ancestral character whose appearance is 
rendered possible by the late formation of interfascicular cambium in the 
stem. The isolated, sporadic, and (often) rudimentary characters of this 
‘ anomaly ’ support my view ; for these are precisely the features which 
distinguish ancestral structures wherever they appear. 
I should-, therefore, regard each bundle of the normal stem of Lygino- 
dendron as itself the 
equivalent of a single 
complete stele in the 
stem of Medullosa an- 
glica , of which the proto- 
xylem, primary centri- 
fugal, and secondary 
tissue belonging to the 
ventral or pith-side of 
the stele have completely 
vanished. I admit the 
bare possibility of what 
I cannot help regarding 
as a quite meaningless 
cambium appearing on 
the scene ; but this me- 
chanical view of the 
matter I regard, in the 
light of the facts cited 
above, with very much 
less favour than the one 
already given. More- 
over, Scott, so it seems 
to me, is inclined to attach a far too great significance to the difference 
existing between primary and secondary tissues. In my opinion there is 
no essential difference between primary meristem and cambium, the difference 
merely lying in the varying periods at which they respectively arise, each 
having, in accordance therewith, its own peculiar characteristics. And 
the secondary tissue is one of the great and characteristic features of the 
group of plants with which we are dealing. 
Owing to the even, uncurved contotir of its ring of secondary xylem 
(Fig. 8) (so contrasted with that of the ring of secondary xylem in Lygino - 
1 Cf. Seward’s c Lyginodendron robustum .’ 
Fig. 8. Heterangium Grievii : transverse section of secondary 
wood of stele of stem, showing entire absence of any curvatures 
save those which are necessary for maintaining the cylindrical 
contour of the stele as a whole (diagrammatic). 
