812 Spratt . — The Formation and Physiological Significance of 
stele. In Podocarpus and Saxegothaea the stele is diarch ; but it may 
remain more rudimentary, as in the small nodules of Microcachrys , where 
frequently only two or three tracheides are present. There is always an 
endodermis. 
7. There is no differentiation of a meristematic zone in the cortical 
tissue. In this respect the nodules of the Podocarpineae differ from the 
nodules of all the other non-leguminous plants with which they asso- 
ciated. 
8. The majority of the cortical cells of the root and nodules eventually 
become water-storage cells, and in some of these the Bacteria remain 
quiescent during the winter. 
9. The Bacteria produce a very definite zooglea in the cells, and in 
these slime threads pass from cell to cell. 
10. The nuclei of the host cells, in Podocarpus , are stimulated by the 
presence of the zooglea around them to elongate and then divide amitotically, 
so that several nuclei are frequently present in one cell. 
11. In the spring the cells immediately below the endodermis at the 
apex of the nodular stele become meristematic and produce new cortical 
cells in the interior of the old nodule. 
12. Successive zones of collapsed tissue surround the new cortical cells 
of the nodule year by year. 
13. In Saxegothaea the meristematic tissue at the apex of the nodular 
stele frequently bifurcates before producing the new cortical cells, with the 
result that there are two centres of tissue formation and two new 
nodules are produced inside the old one, which is eventually ruptured 
and cast off. 
14. The outer empty cells in Podocarpus are sometimes inhabited by 
fungal hyphae, which may be of a mycorhizal nature. 
15. The Bacteria isolated from the nodules are found to be identical in 
structure, and growth in pure cultures, with Pseudomonas radicicola obtained 
from the root nodules of the Leguminosae, Cycadaceae, Elaeagnaceae, Alims, 
and Myrica . 
16. When isolated from the nodule the organism is capable of assimi- 
lating atmospheric nitrogen when grown on suitable media, and consequently 
its presence is undoubtedly beneficial to the plants of the Podocarpineae, 
with which it is associated. 
17. The morphology of the nodules supports the theory that Podo- 
carpus and Saxegothaea are the most widely divergent of the genera in 
the Podocarpineae, and that they are connected through Microcachrys and 
Dacrydium . 
18. The presence of root nodules in Phyllocladus is additional evidence 
for regarding it as a member of the Podocarpineae rather than of the 
Taxineae, or a group intermediate between these two. 
