TRANSACTIONS OF SECTION K. 679 
strands of secondary wood and bast, which formed a network round the steles and 
‘meristeles.” These strands strongly recall those of certain genera of Cycads, 
both as regards their irregular arrangement and occasional inverse orientation, 
and in their minute structure. An accessory vascular strand, similar to those 
of Medullosa anglica and comparable with the cortical bundles of Cycas, is also 
resent. 
F The stem is regarded as possessing a protostele, from which large leaf-trace 
strands (‘ meristeles’) were given off; these latter were ultimately entirely used up 
in the production of concentric foliar bundles of either the radially symmetric or 
unilateral type. The vascular structure is thus brought into closer relation with 
Medullosa anglica. 
The fossil is considered to be of some importance on account of its possible 
affinities with the Cycads, and the suggestion is put forward that it is from such 
a monostelic type as Swtcliffia, rather than from the polystelic members of the 
Medullosez that the origin of the Cycadacezx is to be sought. 
MONDAY, SEPTEMBER 9. 
The following Papers were read :— 
1. Some Inpressions of the Flora of Northern South America. 
By Professor D. H. Campseuu, Ph.D. 
2. The Root-nodules of the Podocarpee. 
By Professor W. B. Bortomtey, M.A. 
Noble and Hiltner in 1899 demonstrated that the root-nodules of Podocarpus 
were concerned with the assimilation of nitrogen. Shibata in 1902 attributed 
the formation of the nodules to an endophytic mycorhizal fungus. Bottomley 
in 1906 showed that the root-nodules of Podocarpus chilina contained nitrogen- 
fixing bacteria similar to those found in the nodules of leguminous plants. 
Root-nodules are found in all the genera of the Podocarpex, viz., Podocarpus, 
Dacrydium, Microcachyrs, Saxegothea, and Phyllocladus, and their structure 
has recently been investigated by Miss Spratt, of King’s College, London. 
The nodules are always arranged in two distinct rows along the sides of the 
roots, and are evidently modified lateral roots, being ceveloped from the 
pericycle cells opposite the protoxylems of the diarch root. Infection and 
subsequent arrest of normal development of the lateral root is caused by the 
entrance of bacteria into the cortical cells through the root-hairs in the first 
instance. 
The mature nodule consists of a central stele which is continuous with that 
of the root, surrounded by a cortical mass of parenchymatous cells containing 
bacteria, and an outer layer of cells which often produces root-hairs. 
The bacterial tissue of the nodule remains active for one season only. 
Towards the end of the season most of the cells lose their contents and their 
walls become thickened by the formation of characteristic bars of cellulose. 
The following spring a new mass of active bacterial tissue is formed by the 
activity of the pericycle cells of the stele, and the old cortical cells with their 
barred cell-walls are squeezed out to form an outer protective zone. Although 
several ‘annual’ zones may be seen in a nodule, the original outermost layer of 
cells of the nodule remains intact, except in the bifurcated nodules of Saxegothaa. 
This formation of fresh bacterial tissue each year is characteristic of all root- 
nodules, both leguminous and non-leguminous, concerned with the assimilation 
of atmospheric nitrogen. 
All the nodules of the Podocarpez are simple structures, with the exception 
of Saxegothaa, which has bifurcated nodules. 
The presence of root-nodules in Phyllocladus supports the contention of Young 
im +e must be regarded as a member of the group Podocarpee rather than of 
the Taxez. 
