A Stigmaria with Centripetal Wood. 
BY 
F. E. WEISS. 
Professor of Botany in the University of Manchester. 
With Plate XV. 
NE of the most striking features in the structure of the Stigmarian axis 
vy is the fact that its primary wood shows, as a rule, a centrifugal 
development, while in the stems of L epidodendron and Sigillaria , which 
formed the aerial continuation of the Stigmarian axis, the primary wood was 
invariably developed in a centripetal direction. 
There seems to be a general opinion that this latter course of develop- 
ment of wood is the more primitive one. Its occurrence in the stems of 
the small number of recent Lycopodiales must perhaps not be taken as 
an argument in favour of this view ; but the existence of this type of 
wood in the Lower Carboniferous Catamites petty cur ensis, in Sphenophyllum , 
and in the Pteridospermeae, where the ‘ old wood ’ may be taken as a pre- 
cursor of the ‘ new wood ’ of the Cycadales (see Scott, ’02), are facts which 
seem to indicate the course taken in the evolution of the vascular system 
in the stem of the higher plants. 
Whether the centrifugal development of the wood in the Stigmarian axis 
is the primitive condition of that organ, or similarly due to a substitution of 
‘ new wood for old has, however, remained an open question. 
It is true a few specimens of Stigmaria have been described with a 
centripetal development of their primary wood, but this character seems 
in no way associated with other primitive characters. On the contrary, the 
Stigmaria Brardii described by Renault (’88) in the first instance as Stig- 
maria fiexuosa , from Tracy St. Loup, near Autun, which, in its outward 
appearance, resembled the Stigmaria rimosa of Goldenberg (’58) (PL XII, 
Fig. 3 ), should, according to Solms-Laubach (’94), be correlated with 
Stigmariopsis , which must probably be regarded as more highly specialized 
than Stigmaria . According to Grand’Eury Stigmariopsis is the basal 
portion of Clatharia and Leiodermaria , forms of Sigillaria. 
As far as I know, no specimen of Stigmaria with centripetal wood has 
been described from the English Coal Measures, and as some importance 
is attached to this arrangement, both as regards the primitiveness of its 
[Annals of Botany, Vol. XXII. No. LXXXVI. April, 1908.] 
