EQUISETUM SPOROPHYTE 3o5 



being the points of insertion of the leaf-sheaths, oppo- 

 site which are various complications of the arrange- 

 ment of the tissues as has already been observed : in 

 the internodes the tissues show greater regularity of 

 arrangement. Note that on passing towards the apex 

 the internodes are successively shorter, and the character 

 of the tissues of both nodes and internodes becomes 

 more uniform : also that the leaf-sheaths become suc- 

 cessively shorter. Following the axis upwards it may 

 be seen to terminate in a sharp cone, which is the 

 punctum vegetationis, consisting of cells undergoing 

 division, which constitute the primary meristem. 

 Here and there it may be seen that lateral buds have 

 been cut through : they are situated at the nodes, and 

 appear to be completely surrounded by the tissues at 

 the bases of the leaves: in their form and structure 

 they resemble the punctum vegetationis of the main 

 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 



