Buds and Stems. 53 



general ground tissue in which the bundles are embedded 

 serves the functions of the pith, medullary rays, and thin- 

 walled portion of the pericycle and primary cortex, as 

 stated for Aristolochia. 



68. Make an outline drawing of the parts of the cross 

 section of the stem of corn and use the colors to designate 

 the same functions which they were made to represent for 

 Aristolochia. Thus the epidermis would be blue as be- 

 fore, the thin-walled cells of the primary cortex green, 

 while its thick-walled cells would be red; the thin-walled 

 tissues in which the bundles are embedded yellow, the 

 phloem purple, the xylem orange, and the narrow zone of 

 thick-walled tissue bordering the bundles red. The colors 

 will assist in comparing the different parts of the stem 

 from the standpoint of their use, blue meaning that pro- 

 tection is given ; green, that food is manufactured, tempo- 

 rarily stored, and slowly conducted away as needed ; red, 

 that strength is imparted; yellow, that food is stored and 

 slowly conducted ; purple, that food materials, and partic- 

 ularly proteids, are rapidly carried either up or down the 

 stem where need is urgent; orange, that water is rapidly 

 carried from roots to leaves; uncolored, that the cells 

 are rapidly multiplying and increasing the diameter of 

 the stem. 



69. Plant seeds of garden balsam in moist sawdust, and 

 keep watered with well water. As soon as the seedlings 

 appear place one lot near a window, and another lot on a 

 side of the room remote from the windows where the light 

 is not intense. Note the difference in rate of growth, in 

 the relative lengths of the internodes, and in the size of 

 the leaves. Do the stems grow upright ; if not, what force 

 is interfering with gravity ? Carefully remove some of 

 both lots of seedlings from the sawdust and place in a 



