222 PKACTICAL BOTANY. 



axis, but on a smaller scale. Note also the irregularly 

 annular or spiral tracheides in the internodes, and the 

 way in which their structure is modified at the nodes, 

 where they appear shorter, and are more closely 

 reticulated. 



Examine the punctum vegetationis under a high 

 power, and observe 



1. At the extreme apex a single, large, wedge-shaped 

 cell ; this is the Apical cell. The cells immediately 

 adjoining it are arranged in regular order, and are of 

 definite form, being Segments successively cut off 

 from the apical cell. Observe how the older segments, 

 which are further from the apical cell, have been suc- 

 cessively divided up by walls perpendicular to the outer 

 surface (anticlinal), and parallel to the outer surface 

 (periclinal). The details of arrangement of the suc- 

 cessive walls may with advantage be traced by com- 

 parison of several preparations, and explained by 

 reference to the Text-Books. Since the superficial cells 

 are subject to repeated periclinal divisions it is clear 

 that there is no definite layer of dermatogen : compare 

 this structure of the punctum vegetationis with that of 

 the lateral buds above mentioned. 



2. Note the leaf-sheaths, successively smaller towards 

 the extreme apex, and observe how they originate by 

 outgrowth and division of successive zones of cells 

 below the apex. 



3. Attention should also be paid to the mode of 

 origin of the lateral buds : a diligent comparison of 

 them in various stages of development will show that 

 they are not of endogenous origin, but are derived from 

 superficial cells lying immediately above the insertions 



