Ie 
1897] CURRENT LITERATURE 139 
were observed to enter the medullary rays and pass outwards, accompanying 
mucilage canals, the xylem and phloem elements joining the corresponding 
regions of the primary zone, the mucilage canals passing on to join the canal 
system of the cortex. As would be expected, this vascular system of the 
pith is. strictly cauline, the mucilage canals appearing unattended near the 
apex, while farther down the accompanying vascular elements are gradually 
differentiated. 
Another cycadean peculiarity, known heretofore in Cycas and Enceph- 
alartos, is the occurrence of a succession of secondary zones of vascular 
Strands outside of the primary leaf-trace zone, formed by successive meristem 
zones developed in the pericycle. In Macrozamia these secondary zones are 
Strongly developed, the first one being as prominent as the normal one, the 
Subsequent ones rapidly diminishing in size. The strands of the secondary 
zones have the same orientation as those of the primary zone, the xylem of 
€ach zone abutting almost directly upon the phloem of the next inner one. 
What Mr. Worsdell apparently regards as a capital discovery, however, is 
the detection of an occasional “tertiary cambium,” by which he means that 
between the primary and first secondary zones, or between successive sec- 
ondary zones, small intermediate bundles are occasionally developed. The 
remarkable thing about them, however, is their reversed orientation, the 
xylem being directed outwards, towards the xylem of the outer zone. This 
Position occasionally results in an appearance so suggestive of a concentric 
bundle that the author associates with it the well known cortical concentric 
bundles of Cycas, and suggests a possible method of the derivation of the 
Collateral bundle from the concentric. He sees in these “anomalous struct- 
ures” of cycadean stems the “ remnants of some ancient structure once com- 
mon to a large group of plants,” this ancient structure consisting of “rings 
or layers of concentric vascular strands.” Later, the meristem of the inner 
portion of each concentric strand gradually, became less and less functional, 
that of the outer portion became more and more active, and the collateral 
bundle was developed. These rings of ancient concentric bundles are still 
Seen in the cortex of Cycas, and the reduced inner portions of the concentric 
bundles are seen in the small intermediate bundles of Macrozomia with 
Teversed orientation. This hypothesis will be tested, not only by further 
€xamination of living cycads, but also by an investigation of the structure . oe 
‘Rumerous fossil forms which are either cycads or show cycad affinities. — 
EMC. 
‘Dr. D.H. CAMPBELL a year aise described in this joins a new genus 
: of liverworts, to to which he gave the name Geothallus tuberosus. it caeta id 
tena a other 
more nearly than with any 
tied ‘These two genera, along. with Riella and T rh allo 
tAwrc 
Loan ee oR ‘ mao hy RMR Pe Bus 
“or. Gas, a: os Hs > i806. 
