8o 8 Spratt . — The Formation and Physiological Significance of 
environmental conditions are again favourable for their activity, and also 
that of the host plant (Figs, n, 12, and 16). 
The following spring, in the nodules of all the genera of the Podocar- 
pineae examined, some of the cells immediately below the endodermis 
at the apex of the vascular strand of the nodule become meristematic 
(Fig. 12). A rapid formation of new tissue ensues in the centre of the 
nodule, pushing out and crushing the old water-storage tissue, which now 
readily collapses. The formation of new tissue beneath the endodermis 
causes the rupture of the latter, but later, when the rapid cell division ceases, 
a new endodermis is differentiated around the apex of the stele (Fig. 13). 
The Bacteria resume their activity and are stimulated to produce numerous 
infection threads, which penetrate into the newly formed cortical cells 
(Fig. 13). In this way living, active cortical cells are produced inside the 
old tissue of the nodule, which now forms a protective covering around the 
new nodule. This formation of a meristematic zone at the apex of the 
vascular cylinder, and the consequent production of new internal tissue, 
recurs year after year, so that a number of successive protective layers are 
formed around the active cortical cells by the annual displacement and 
collapse of the tissue formed the previous year (Fig. 14). The outermost 
zone in all the nodules always remains intact, being composed of a few 
layers of cells which are part of the first year’s growth. It is this zone 
which has the capacity for producing hairs if occasion arises. The tissue 
produced in succeeding years becomes very crushed, and often, as in 
Microcachrys and Saxegothaea , almost obliterated, except at the base, 
just around the vascular strand, where the annual additions are always 
apparent. 
In Saxegothaea conspicua , where the branching of the root is extremely 
prolific and the nodules are produced side by side in very close proximity 
to one another, the nodules have frequently been observed to branch (Figs. 
7, 18, and 19). In the spring, when the meristematic zone arises at the 
apex of the vascular strand, bifurcation of the zone takes place (Fig. 18), 
with the result that the nodule at first appears to have a branched stele ; 
but later a distinct zone of cortical cells is produced by the apex of each 
branch of the stele. In this way two new cortical zones centred round 
a portion of the stele are produced inside the original nodule (Fig. 19), and 
these, at first, compress the tissue formed the previous year or years, and by 
their united activities eventually break through it. The tissue of the 
original nodule thus becomes ruptured and later is cast off ; the two nodules 
produced in its place are each complete, independent structures, which 
subsequently develop according to the usual method described above. The 
capacity which the nodules in this genus have for branching gives the root 
its characteristic coralline, rather than beaded, appearance, a very large 
number of nodules being produced around the root eventually by their 
