594 A TEXTBOOK OF THEORETICAL BOTANY 



which is formed anew every year and pushes outwards the dying remains of 

 the zone formed the previous year, which then rots off. The cortical cells 

 are used for storage and are filled with starch grains. 



Leaf trace 



^J 



Cambium 



Trachei 



'"" ' -^j^pMiy ' :'} 



'^s ^ ' ""*' ^vvyM^^^ '.''i !^-^ *'^^w!^'^B ^* ' "" * ''' 



" - ^ ■'• . • • ♦ • • , '^'^' ♦ • ; -m^ ,. • '» ^ 



Prismatic tissue sm 



t^'*' 



T" 



rf* '*' »*• 







» ^» ". ^'t* ,'1. ?i^. •" ^«i'-i t» ^„'t .* - .- ._^„ J». 



V 



Fig. 6o2. — Isoetes lacustris. Transverse section 

 of stem showing the structure of the stele. 



Root 

 trace 



Fig. 603. — Isoetes hnustris. Transverse section of the entire stem showing 

 the two-lobed structure and the replacement of old cortex by new 

 cortex. 



From the upper part of the stele arise the leaf traces, one to each leaf, 



which curve upwards and outwards through the secondary cortex (Fig. 604). 



The stem apex though sunken between the stem lobes, is itself flat and 



