50 LABORATORY AND FIELD EXERCISES 



HERBACEOUS STEMS 

 DICOTYLEDONS 



Study the main layers of herbaceous stems in transverse 

 section, contrasting them with similar layers of the woody 

 stems studied above. 



1. Epidermis. Is the epidermis present ? What is the color 



of herbaceous ste'ms ? Are they smooth or rough ? 

 Compare the external features of woody and herba- 

 ceous stems. 



2. Bark. What are the layers of the bark (using the term bark 



to include all tissues from the epidermis to the cam- 

 bium) ? Contrast these tissue layers with those of woody 

 stems just studied. What is the function of green bark ? 



3. The wood cylinder. How does it differ from that found 



in woody stems ? Is it an unbroken cylinder ? Is 



it as thick as that of woody stems ? Are there annual 



rings ? How do you explain your findings on this 



point ? Stain your section with iodine and observe again 



the tissues of the wood cylinder. Note the following : 



a. Dead tissues and cells. Do these appear to be similar 



to those of a woody-stemmed plant ? If they are 



different, be prepared to explain how and why. Why 



can an herbaceous plant get along with a smaller 



amount of wood tissue than a tree or a shrub ? 



1>. Living tissues of the wood. How are these distributed 



in herbaceous stems ? Compare with the distribution 



of similar tissues in woody stems. Compare the 



amount of living storage tissues in herbaceous and 



woody stems. 



c. Pith. Note the relative size of the pith in herba- 

 ceous as compared with woody stems. Is there a 



