THE AUSTRALIAN NATURALIS'T, . 193 
growths, tubercles, or, as they are more popularly known, 
nodules, If these plants, or éven their roots, decay in the 
soil, the assimilated nitrogen passes to the soil in a form 
readily available to plants. The change from available to 
non-available nitrogen ig brought about under normal con- 
ditions by certain soil bacteria. The result of the legumin- 
‘ous crop is thus to pass to the soil the equivalent of a dressing 
of nitrogenous manure. The nitrogen becomes slowly avail- 
able, and has a longer period of effectiveness, and the soil 
further improves in texture as a result of the incorporation 
of humus. These facts are largly availed of in agriculture 
in the use of green manuring and soiling crops. 
Nodules Non-leguminous Plants. Besides those on leoumes, 
‘similar nodules are known in certain Hleagnaceae, Alnus (the 
Alder tree), Podocarpus, and the Cycadeae. Instead of being 
growths on the roots in these cases, the nodules are formed 
by distortion of the rootlets: This is probably the origin also 
of the recently discovered nodules on the River Sheoak (Ca- 
suarina Cunninghamiana),. 
Scientific investigation or leguminous nodules has been al- 
most entirely confined to the great pea-flowered sub-family 
(Papitionaceaz). Of this group only the Honey Locust 
‘tree (Gleditschia triacanthos) has been found free from 
nodules. : 
Recently it has been shown that nodules are characterictic 
of all the sub-families. The following; list of Australian le- 
gumes found to carry nodules has been compiled from the 
notes of several observers, and goes to show that the posses- 
sion of nodules is as characteristic of our legumes as of those 
of other countries. 
In seven cases (indicated +), the bacteria have been demon- 
strated. In the others the nodules have been considered 
‘sufficient evidence of the symbiosis. 
PLANTS BEARING ROOT-NODULES. 
Acacia rubidat—G.P.D.S.* ; W.M.C. (Lawson). 
decurrens—C.T.M.§ and W.M.C. (Richmond). 
i war mollissimat—GrP.D.S.* 
melanozylon—W .M.C. (Kurrajong Heights). 
discolor—C.T.M.§ (Kurrajong Heights) ; W.M.C. (Hun- 
ter’s Hill). 
suaveolens} —G.P.D.S.*; W.M.C. (Terrigal) ; C.T.M.§ 
(Bick d); W | 
linearis—O.T.M. (Richmond) ; W.M.C. (Terrigal). 
stricta—W.M.C. (Terrigal). sagerneal) 
pruinosa—W .M.C. (Terrigal). 
