124 



BOTANICAL GAZETTE 



[august 



dense cell contents. Late in the history of the plant the pericycle 

 becomes lignified. There is no differentiated endodermis in either 

 old or young stems. 



In the cortex of the young stem is a continuous band of tissue 

 7-8 cells wide, which responds to the test for suberin (Tun- 

 mann 16). This is in patches in the older stems. The intercel- 

 lular spaces of the pith are very large. 



Figs. 13-15. — Fig. 13, young stem of P. methysticum after differentiation has 

 been completed, X80; fig. 14, petiole, X101; fig. 15, sector of stem after interfascicular 

 cambium has been developed, X101. 



Secondary activity in the stem 



There are two methods by which the stem of Piper methysticum 

 enlarges: (1) by active division of pith cells; (2) by cambail 

 activity. 



1. In the center of and at irregular intervals throughout the 

 pith, groups of cells will divide actively throughout the internode. 



