ZEA MAYS 



1X7 



through the internode. Upon entering the node, some pass directly 

 downward near the periphery of the stem and are almost radially 

 perpendicular; while others penetrate the stem more deeply, fol- 

 lowing a horizontal course. These may at first even incline 

 slightly upward and then curve downward toward the periphery, 

 where they become almost vertical. All of the bundles descend 

 through two or three or more internodes without branching or 

 anastomosing with other bundles. 



Fig. 51. Section of the sixth internode of the stem : an v, annular vessel ; bu sh, bundle 

 sheath ; ep, epidermis ; lac, lacuna ; mph, metaphloem ; mx, metaxylem ; par, parenchyma ; 

 /I/'/', protophloem ; /)x, protoxylem ; j/» f, spiral vessel ; /r^, tracheids. (After Avery.) 



As a result of the anastomoses of descending bundles with those 

 which enter the stem at lower nodes, the total number of bundles 

 in the lower internodes is approximately the same. Hershey and 

 Martin (9) investigated the development of the bundles in yellow 

 dent corn and found that 90 per cent of them were differentiated in 

 the lower internodes by the forty-fifth day. The number formed 

 at maturity was 680 for the first internode and 750 for the second. 



Since the entering bundles incline toward the periphery of the 

 stem in their downward course, they are more crowded near the sur- 

 face than in the central portion of the axis. (Fig. i5.) The in- 

 clination of the bundles toward the periphery is not readily detected 



