52 



Introduction to Botany. 



of tissues seen in the cross section of the stem, simply out- 

 lining them in right position and proportion, and with the 

 colored pencils give each part having a distinct function a 

 color of its own. For instance, color the epidermis blue, 

 the thick-walled cells of the primary cortex red, and its 

 thin-walled cells green, the strengthening ring of the peri- 

 cycle red, the inner portion 

 of the pericycle, medullary 

 rays, and pith yellow, the 

 phloem purple, the xylem 

 orange, and leave the cam- 

 bium uncolored. Run dotted 

 lines from the different parts 

 and at the end of each line 

 write the name and function 

 of the part. 



6'j. Make sections of the 

 stem of Indian corn where 

 it is about one centimeter in 

 diameter, and treat as di- 

 rected for Aristolochia. Here 

 the bundles are scattered 

 promiscuously throughout 

 the stem, and there is no distinction into pith and medul- 

 lary rays (Fig. 20). The stem is given strength by the 

 thick-walled cells of the primary cortex lying at the periph- 

 ery, and by a sheath of somewhat similar cells around 

 each bundle. The vascular bundles consist of the same 

 parts as those of Aristolochia, the xylem facing the center 

 and the phloem the circumference. There is, however, 

 no cambium between the two parts of the bundle, and the 

 latter does not therefore increase indefinitely in size, but 

 soon attains to its maximum dimensions. In corn, the 



Fig. 20. 



Cross section of a stem of Indian com. 

 fl.epidermis; ^.primary cortex; ^.peri- 

 cycle; d, vascular bundle; e, ground 

 tissue. 



