CRYPTOGAMS 701 



by repeated tangential division of their cells ; the layers in question thus 

 undergo a well-marked change of function with advancing age. In 

 Thalassiophyllum, according to Rosenthal, the "formative" layer of 

 photosynthetic tissue (Bildungsschicht) gradually loses its meristematic 

 activity and dies, whereupon a second cambial layer arises by tan- 

 gential division in the peripheral portion of the "outer cortex." In 

 several Laminakiaceae the secondary tissues are arranged in concentric 

 strata, which recall the annual rings of a Dicotyledonous stem. 



