*5* 
R. S. Adamson. 
a phelloderm, are cut off internally by the phellogen, and add to 
this tissue. Crystals of calcium oxalate occur in some of the 
cortical cells, especially in the inner ones (Fig. 4). 
Fig. 4. Transverse section of root, showing lacunae in secondary phloem. 
Structure of the Vertical Roots. 
In general structure these are very like the horizontal roots, 
but on a smaller scale. They differ from ordinary pneumatophores 1 
in being freely branched, the branches arising endogenously in the 
normal manner ; like the horizontal roots they are at first triarch, 
with additional protoxylem groups appearing later. 
Near the apices of these roots the cortex is simple with a few 
1 Karsten. Bibliotheca Botanica, XXII., 1891. 
