338 Knox: Strem OF IBERVILLEA SONORAE 
A section at the base of a stem two and a half centimeters in 
diameter shows a new feature of considerable interest. This is the 
appearance in the medullary rays of supernumerary leptome-bundles 
which Pitard (30) calls tertiary bundles, consisting of semicircular 
meristematic areas of which the long axes of the meristems are 
FicurE A. Jbervillea Sonorae in its native habitat.* 
parallel with the medullary rays, so that the axis of any bundle is 
at right angles to that of the primary bundle next to it. The 
bundles frequently appear to be collateral and contain hadrome 
elements on the side next the wood of the primary bundles. The 
phenomenon is one not infrequently found among the Czcz bitaceae, 
* This photograph 4 was used for plate 16 of Carnegie Inst. Publ. No. 6. 
