36 



Myxophycex 



in the soil, and that it entered the roots regularly at the beginning of every 

 autumn through the lenticels. Spratt ('11) confirmed the fact that the Alga 

 entered the roots through the lenticels, and showed that this was accomplished 

 by means of gonidia which were developed from heterocysts and spores 

 present in the soil. There is no doubt in this case of the symbiotic relationship 

 between the Alga and the two nitrogen-fixing Bacteria, and there is every 

 probability that the Cycads benefit to some extent by being able to absorb 

 certain products of the metabolic activity of the lower organisms. Needless 

 to say, both the above species of Anab&na are considerably different from 

 the more normal species of the genus, and both have degenerated. 



An endophytic member of the Nostocacea? also lives in the hollow 

 leaf-auricles of the Hepatic Blasia, but its exact relationships with its 



>o.c. 



a.z 



i.e. 



Fig. 22. Part of a transverse section of tubercle-like root of Cycas showing the algal zone (a. z.) 

 containing Anabsena Ci/cadearum Eeinke and certain Bacteria, c., cork; o.c., outer cortex; 

 i.e., inner cortex, x 400 (modified from Spratt). 



peculiar environment have not yet been investigated. Another occurs 

 in the stems of Gunnera. 



Hugo Fischer ('04) has described a symbiotic relationship between 

 certain of the Oscillatoriaceae which carpet the ground (such as Phormidium 

 autumn ale) and Azotobacter Chroococcum. The nitrogen-fixing activity of 

 the Bacterium enables the Blue-green Alga to make use of atmospheric 

 nitrogen. 



A still more remarkable member of the Nostocace* is Richelia intra- 

 cellularis Johs. Schmidt, which lives within the cells of marine species of 

 Rhizosolenia (fig. 23). As this Alga occurs within the living cells of the 

 host it may be assumed that it is a partial parasite. 



