Growth. 



IS 



3. Elongation of the stem of a monocotyledonous 

 plant.— Mark the stem of a young plant of corn {Zea), wheati; 

 {Tritiium), or any tall grass, with India ink, at intervals of one 

 centimeter, as in the previous experiments. Measure on the 

 following days, and find the zone of maximum growth ; also 

 locate the portions in which the separate internodes elongate 

 most rapidly. Compare with similar data obtained from a 

 dicotyledonous stem. 

 Measure the length of 

 the internodes of a 

 mature cornstalk, and 

 note the region in which 

 the greatest length is 

 attained. Cut across 

 the stem in several 

 places, and measure the 

 diameter of the various 

 bisected internodes. In 

 what portions of the 

 stem is the greatest 

 diameter obtained ? 



Note the manner in 

 which a growing grass 

 stem comes apart when 

 stretched in theTlands. 

 contain the mechanical! 



Fig. 6. — Diagram of cross-section of stem of 

 Xea. ec, cortex and epidermis ; /, phloem ; ^, 

 xylem ; y, sclerenchyma. After Bonnier and 

 Leclerc du Sablon. 



The zones of maximum 

 strengthening 



grow th 

 is 



tissues, and it 



torn apart. 



at these places that the stem is most ' easily 



Observe also the manner in which the sheathing bases of the 



leaves surround and protect the delicate tissues (Fig. 5). 



4. Arrangement of the tissues of a monocoty- 

 ledonous stem. — Cut a thin cross-section of a young stem of 

 com [Zea), and examine with a magnification of 60 diameters. 

 Note the position of clumps of denser tissu e, the fibrovascular 

 bundles. They will be found scattered irregularly in the sec- 



