HirsH: AIR CHAMBERS IN THE RICCIACEAE 77 
becomes imbedded by an upward growth of the surrounding tissue, 
so in,the case of the latter the bottom of the pit becomes sunken 
in the3thallus by similar growth. 
From what has been said it is evident that there are two 
methods of origin of the air spaces in the Ricciaceae : the first, by 
partly closed. 
internal cleavage, resulting in the formation of broad, irregular, 
chamber-like spaces separated by plates of green cells one layer 
thick; the second by the upward growth of filaments at right 
angles to the surface of the thallus, resulting in the formation of 
elongated, narrow air chambers. The two species studied by 
Barnes and Land represent only Récciella and Kicciocarpus, in 
which groups the origin of the air chamber is by internal cleavage. 
R. Frostii Aust., on the other hand, is a true Riccza, in which the 
air chambers are formed by the growth of filaments at right angles 
to the surface. 
This work was done in the botanical laboratory of Cornell 
University at the suggestion and under the supervision of Dr. E. 
J. Durand. 
