52 LANG, Stele of the Shoot of Isoetes Incus iris. 



PLATE II. 



Photo 4. Longitudinal section through the apical region of 

 another plant, showing the relation between the pro- 

 cambial regions and the differentiated stele. ( x 130.) 



Photo 5. Transverse section through the stele of a plant with a 

 well-marked secondary zone. ( x 67.) 



Photo 6. Transverse section of the stele of the same plant 

 showing the primary differentiation complete, but no 

 secondary growth. ( x 130.) 



Photo 7. Transverse section from the same plant showing the 

 differentiation of the stele almost complete. ( x 130 ) 



Photo 8. Transverse section from the same plant still nearer to 

 the apex, showing the stele just delimited but still un- 

 differentiated. A central and a peripheral region can 

 be distinguished in the still meristematic tissue. The 

 only lignified elements are the protoxylem of a leaf- 

 trace (t>x) in the peripheral region. ( x 130.) 



