ANABAENA. 545 



zone generally forms a circle; in longitudinal section the cylinder 

 of blue-green algae does not extend quite up to the growing 

 point. According to Eeinke, the alga penetrates into the 

 newly-formed intercellular spaces of the developing periblem- 

 cortex, and remains confined to the zone which it has first 

 excited to increased growth. It is not certain whether the 

 Nostoc penetrates only into injured places or into natural 

 fissures. 



The branched aerial masses of tubercles on Cycad-roots are 

 produced independently of the Nostoc} but their function is 

 unknown beyond a suggestion that they are organs of respira- 

 tion. They certainly receive no injury from invasion by the 

 Nostoc. Since the Nostoc lives completely cut off from the outer 

 world and frequently in subterranean roots, we must assume 

 that it receives nourishment from the host. 



Eeinke found Anahacna in roots of Gycas, Ceratozamia, Dioon, 

 and Encephalartos. 



Eeinke has also found very fine fungal mycelia in the roots 

 of Cycads. Schneider observed intracellular bacteria in root- 

 tubercles free from Nostoc. 



Anabaena azollae Strasb.^ This endophyte is never absent 

 from Azolla, neither A. caroliniana so much cultivated in hot- 

 houses, nor the wild species found in America, Africa, Asia, 

 and New Holland. The algal filaments are present even in 

 the neighbourhood of the vegetative point and in the closed 

 indusia of the sporangia. They are, however, most abundant 

 in the cavities formed in the epidermis of the fleshy floating 

 leaves.^ The AnabaeTia filaments do not enter the cavity by 

 the opening found in the completed structure, but find their 

 way in during the formation of the cavity, and probably influence 

 its development. As the cavity becomes filled with Anabaena, 

 some cells of its inner walls grow out as segmented branched 

 filaments amongst the coils of the alga, probably in consequence 

 of a stimulus exerted by the Anabaena. 



No endophytic Schizophyceae are known in the true mosses, 



1 Moebius {loc. cit.) states that the roots of Cycads at the Botanic Garden, 

 Heidelberg, never contain Anabaena. 



2 Strasburger, Ueber Azolla, Jena, 1873 ; also Practical Botany (English Edition 

 by Hillhouse, 1889). 



'The leaves of Azolla are divided into two parts, the upper fleshy one of 

 which floats on the water, the under membranous one being submerged. 



2m 



