Relation of Ptendosperm Anatomy to that of Cycads. 45 
time they divide. This constitutes an unimportant difference from 
Hetercingium. As in that genus, however, the bundles remain 
collateral until they enter the petioles, having the appearance, 
according to Scott, of some of the partly-fused petiolar bundles of 
Cycads (14, pp. 364-365; Figs. 132, 133). In the petioles they 
become concentric in all cases, whether the twin bundles of the 
traces fuse again or remain separate (Fig. 3). 
From the foregoing descriptions, it will be seen how similar 
Lyginopteris is to Hetercingium —the mesarch nature of the primary 
xylem strands ; the essential characters of the mesarch leaf-traces 
and petiolar strands; and the general histology of both types, 
indicate a close relationship between them. The chief anatomical 
Fig. 3 .—Lygmopteris oldhamia. Transverse section of rachis. xy, V-shaped 
xylem ; ph, phloem completely surrounding xylem ; px, protoxylem. (Adapted 
from Williamson and Scott, 1895). 
difference lies in the fact that Lyginopteris possesses a pith, while 
the centre of the stele in Heterangium consists of tracheides and 
conjunctive parenchyma. According to Scott, Lyginopteris is “ a 
Heterangium which has acquired a pith,” (14, p. 646) owing to the 
progressive tendency to restrict water-conduction to the new or 
centrifugal wood, thus rendering development of the old primary 
centripetal wood unnecessary (cf. 12). 
Occasionally specimens of Lyginopteris have been observed to 
exhibit anomalies in anatomical structure ; from the present point 
of view, the most interesting variation consists in the formation of 
secondary vascular tissues with inverted orientation, in the pith 
immediately within the normal ring. Sometimes the anomalous 
