1 6 LANG, Morphology of tJie Stock of Isoetes lacustris. 



removed from the median plane to miss the primary stele 

 of the stem. The section in Fig. 3 C cuts across the 

 extension of the rhizophoric stele. The secondary pris- 

 matic tissue seen above this belongs to the base of the 

 stem stele and has allowed of the extension of the rhizo- 

 phoric stele in the plane of the groove. The section in D 

 passes just outside the tip of this arm of the rhizophoric 

 stele and shows the arrangement of the root-traces in the 

 rhizophoric cortex below the groove. Scattered leaf- 

 traces are seen in the upper region of the cortex in this 

 and the other sections in Fig. 3. 



J^ 



Fig. 4. — Outlines of median longitudinal sections in the plane of 

 the groove through two stocks of Isoetes lacustris. 

 Description in the Text. 



Longitudinal sections in the plane of the groove 

 follow the extension of the rhizophoric stele. Just out- 

 side the convex edge of this lies the meristem, which 

 determines on the one side the increase of the vascular 

 tissue and on the other the, production of new roots and 

 the growth of the cortex of the rhizophoric region. Out- 

 lines of longitudinal sections of two stocks in this plane 

 are given in Fig. 4. In these the distinction is evident, 

 not only between the stele of the stem and the rhizophore, 





