gor] TUBER-LIKE ROOTLETS OF CYCAS 271 
of the nostoc forms within the tubercles of the cycads in assist- 
ing nitrogen assimilation. 
In conclusion, therefore, the tubercles of cycads may be 
said to have at least two functions, that of aerating, and that of 
' assisting in nitrogen assimilation. 
THE UNIVERSITY OF CHICAGO. 
