Spratt .— The Root-Nodules of the Cycadaceae. 625 
lo. The Cycadaceae, a group with many primitive characters, are 
the only nodule-bearing plants known, in which four organisms are 
associated together symbiotically, viz. two nitrogen-fixing Bacteria, an 
Alga, and the Cycad. 
Bibliography. 
Bottomley, W. B. : The Cross Inoculation of the Nodule-forming Bacteria from leguminous and 
non-leguminous Plants. Report, British Association, 1907. 
-: Some Effects of Nitrogen-fixing Bacteria on the Growth of non-leguminous 
Plants. Proc. Roy. Soc., B., vol. lxxxi, 1909, p. 287. 
--———--: The Root-Nodules of Myrica Gale . Ann. of Bot., vol. xxvi, 1912. 
Life, A. C. : The Tubercle-like Roots of Cycas Revoltita. Bot. Gaz., vol. xxxi, 1901. 
Osborn, T. G. B.: The Lateral Roots of Aymleon radicans, and their Mycorhiza. Ann. of Bot., 
vol. xxiii, 1909. 
Reinke, J. : Parasitische Anabaena in Wurzeln der Cycadeen. Gott. Nachr., vol. cvii, 1872. 
Schneider, A. : Mutualistic Symbiosis of Algae and Bacteria with Cycas revoluta. Bot. Gaz., 
vol. xix, 1894. 
Spratt, E. R.: Some Observations on the Life-history of Anabaena Cycadaceae. Ann. of Bot., 
vol. xxv, 1911. 
-: The Morphology of the Root-tubercles of Alnus and Elaeagnus , and the Poly¬ 
morphism of the Organism causing their Formation. Ann. of Bot., vol. xxvi, 1912. 
-: The Formation and Physiological Significance of the Root-Nodules in the Podo- 
carpineae. Ann. of Bot., vol. xxvi, 1912. 
Zach, F. : Studie liber Phagocytose in den Wurzelknollchen der Cycadeen. Osterreich. Bot. 
Zeitschr., vol. lx, 1910. 
DESCRIPTION OF PLATE XXIX. 
I — lenticels; r. t. — root-tip; r. — root; n. — nodule; v. b. = stele ; g.p. — meristematic 
apex; p . = phellogen ; f. — cortex ; b. = cells containing bacteria ; a. = loose outer cells; 
c. = periderm ; B.r. — Bacillus radicicola ; Az. = Azotobacter; An. = Anabaena; s. = starch; 
0. = calcium oxalate. 
Fig. 1. Roots of Cycas circinalis, some (n.) negatively geotropic owing to infection with 
Bacillus radicicola. Nat. size. 
Fig. 2. Root-nodules of Cycas circinalis. Nat. size. 
Fig. 3. Root-nodules of Encephalartos Hiidebrandtii. Nat. size. ( a ) large tip without an algal 
zone ; ( b ) branched nodule without an algal zone ; (V) cluster with zone developed. Nat. size. 
Fig. 4. Root-nodules of Stangeria Schizodon (a) without algal zone; (p ) with algal zone. 
Nat. size. 
Fig. 5. Root-nodules of Zamia Lindeni. Nat. size. 
