STIGMARIA. 135 
The annexed figure, Zign. 37, represents the transverse 
section of a small Stigmaria, with the axis displaced from 
its natural situation ; this circumstance, as well as the cor- 
responding external groove, has arisen from compression, by 
which the tough cylinder has been forced from its original 
position in the middle of the soft cellular tissue, to one 
side. 
The central axis is thus shown to be a cylinder composed 
of bundles of vessels, disposed in a radiating mauner, and 
T.1Gn. 37. TRANSVERSE SECTION OF STIGMARIA FICOIDES; nat. 
(M. Adolphe Brongniart.) 
This specimen shows that the cylinder (a in Lign. 36) is formed of bundles 
of vascular tis®te, disposed in rays. 
separated from each other by medullary rays; the whole 
constituting a ligneous zone resembling that of Sigillaria 
(see Lign. 35); but the inner circle of medullary tissue 
seen in the latter is altogether wanting. This difference is 
similar to that observable in the stems or branches of a 
dicotyledonous tree, in which the woody cylinder is asso- 
ciated internally with bundles of medullary tissue, and the 
roots of the same tree that are destitute of them. Part of a 
vascular bundle from the woody tissue of a Stigmaria, seen 
