BIOLOGY OF HIGHER SEED PLANTS 



51 



difference be- 

 tween the two 

 stem types in 

 this respect ? 

 4. Drawing. Draw 

 a sector of 

 an herbaceous 

 stem in out- 

 line, to show 

 the real posi- 

 tion and rela- 

 tive width of 

 the main tissue 

 layers of the 

 bark, the wood, 

 and the pith. 

 Label each of 

 these layers, 

 using terms 

 corresponding 

 to those pre- 

 viously used in 

 the study of 

 woody stems. 

 Point out the 

 main contrast- 

 ing points be- 

 tween woody 

 stems and her- 

 baceous stems. 

 Consult the 

 summary in the 

 text (p. 108). 



FIG. 14. Transverse (A) and longitudinal (B) 



sections of the stem of the sunflower (Helian- 



thus annuus) 



A : e, epidermis ; col, collenchyma of the cortex ; 

 p, parenchyma of the cortex ; b, fibrous phloem ; 

 s, sieve portion of phloem : c, cambium ; fv, ducts 

 of the xylem portion of the fibrovascular bundles. 

 B : f, fibers of the xylem ; t, dotted duct ; (,' scalar- 

 iform duct ; pa, wood parenchyma ; t", reticulated 

 ducts ; s, spiral ducts ; p, thin-walled cells of the 

 pith. After Miiller 



