Some Observations on the Life-history of 
Anabaena Cycadeae. 
BY 
ETHEL ROSE SPRATT, B.Sc., A.K.C. 
Demonstrator in Botany at King's College , London. 
With Plate XXXII. 
AMONG the members of the Cyanophyceae perhaps none are more 
/i interesting than those which are found endophytic in certain other 
plant structures. The best known examples of these are Anabaena Azollae , 
inhabiting the leaves of Azolla ; Anabaena Cycadeae , living in the modified 
roots of Cycas ; and the Nostoc sp. associated with the thallus of Anthoceros 
and Blasia. In each of these cases the region occupied by the Alga is an 
intercellular space. In Cycas this space is in the form of a zone between 
the cortical cells, just below the epidermis, known as the algal zone, which 
Bottomley has shown always contains living in it two kinds of nitrogen- 
fixing Bacteria, Pseudomonas radicicola and Azotobacter , in addition to the 
Anabaena. Considering, therefore, the highly specialized habitat in which 
the organism is found, and the probable symbiotic relationship existing 
between the Anabaena and the two species of Bacteria, the life-history of 
this Alga provides a very interesting subject for investigation. 
Material and Methods. 
The root tubercles of Cycas are found to retain their vitality for weeks, 
and even months, if they are wrapped in moist blotting-paper and kept in 
a tin box. This keeps them in a healthy condition for a surprising length 
of time, and by examining portions of the algal zone from time to time, 
the various stages constituting the life cycle of the Anabaena may be 
observed. 
Several methods were employed to induce the organism to grow in an 
artificial medium, but with very varied success. The most promising 
medium was water containing some sap, obtained by crushing a few Cycas 
roots and tubercles. Solutions containing inorganic salts were not at all 
successful. To some of the former medium i % agar-agar was added, 
the solution boiled and subsequently cooled, so that a solid medium was 
[Annals of Botany, Vol. XXV. No. XCVIII. April, ign.] 
