STIGMARIA 249 



the secondary wood. In the ill-preserved middle cortex 

 the rootlet-bundles are often met with, and here their 

 course seems to have approached more nearly to 

 the vertical. The parenchyma immediately surround- 

 ing the bundle is often preserved when the general 

 cortical tissue has perished. In this region the 

 sectional form of the xylem of the rootlet is triangular, 

 with protoxylem at the apex. At the opposite side 

 the phloem can sometimes be recognised. 



On entering the outer cortex the bundle again takes 

 a more horizontal course. It is ! here surrounded by a 

 well-marked zone of tissue, in which layers correspond- 

 ing to the inner and outer cortex of the free rootlet 

 can already be distinguished. In passing through the 

 periderm the parenchymatous tissues of the base of 

 the rootlet kept pace, by tangential divisions, with the 

 growth of the surrounding secondary zone (Fig. 100). 



Fig. 100 shows, in longitudinal section, the structure 

 of the rootlet at its base, where it is just escaping from 

 the cortex of the principal axis, which is shown in 

 transverse section. At its attachment, the rootlet is a 

 solid structure with its tissues complete, but as soon 

 as it t becomes free the inner and outer cortex are 

 separated by a wide lacuna, in which only slight 

 remains of the probably trabecular tissue, which once 

 occupied it, can be traced. The outer cortex is con- 

 tinuous with that of the main organ, the hypoderma 

 extending over from one to the other without change 

 (Fig. 1 00, o.c). The inner cortex, enclosing the vascular 

 strand, is seated directly on the solid tissue of the 

 transitional region. The continuity of the outer tissues 

 from the main axis to the rootlet appears to prove that 



