The Formation and Physiological Significance of 
Root Nodules in the Podocarpineae. 
BY 
ETHEL ROSE SPRATT, B.Sc., A.K.C. 
Demonstrator in Botany at King's College , London. 
With Plates LXXVII-LXXX. 
HE assimilation of atmospheric nitrogen by plants, belonging to 
A families other than the Leguminosae, which possess structures on 
their roots known as nodules, has long been recognized in the Cycadaceae, 
Elaeagnaceae, Almts , and Podocarpus. Quite recently, too, Bottomley has 
shown that the root nodules of Myrica Gale are intimately associated with 
the fixation of free nitrogen. 
Nobbe and Hiltner, in 1899, demonstrated that the nodules of Podo- 
carpus were active agents in the utilization of atmospheric nitrogen. In 
their experiments it was found impossible to cultivate plants of Podocarpus 
in the absence of the fungus which caused the nodule formation, but plants 
possessing nodules were grown for five years in quartz sand from which 
nitrogen was entirely absent, and during this period they remained perfectly 
healthy and grew well. 
The earlier observers failed to demonstrate the presence of Bacteria in 
the nodules of these non-leguminous plants, but they found numerous 
hyphal-like structures in them, which they considered to be the hyphae of 
a mycorhizal fungus forming a symbiotic association with Podocarpus . 
Shibata described a mycelium, composed of non-septate hyphae possessing 
numerous nuclei, as being present in the cortical cells of the nodule. His 
investigations showed that these hyphae are eventually disorganized and 
absorbed, through the agency of a proteolytic ferment, by the host cells. 
These and similar observations in connexion with Alnus , Elaeagnus , and 
Myrica led to the idea that the formation of the nodules of non-leguminous 
plants was caused by the presence of an endophytic mycorhiza. More 
recent investigations, however, have shown this idea to be erroneous in 
some cases. Bottomley, in 1909, isolated and grew the nitrogen-fixing 
organisms P seudomonas radicicola and Azotobacter from Cycas tubercles, 
[Annals of Botany, Vol. XXVI. No. CIII. July, 19x2.] 
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