CHARACE.E 411 



The general features of Nitella are similar to the above : note 

 however its more transparent appearance, and the presence of only 

 one node on each leaf, while two axillary buds commonly appear in 

 each whorl. They are sometimes incrusted with lime, but are 

 commonly free from it. The sexual organs are borne in groups 

 of three, including two antheridia and one oogonium. 



II. Mount a young part of a plant, including at 

 least one whole internode and two nodes, in water : 

 examine under a low power, and observe : 



1. The cylindrical stem; the internode is covered 

 externally by a small-celled cortex, which surrounds 

 one very large internodal cell. Note that the cortex is 

 composed of (a) elongated cells, and (5) short cells which 

 project as hemispherical bosses, the whole being 

 disposed in spirally curved rows. 



The fact that the cortex invests a large central cell should be 

 verified by cutting transverse sections : these may be prepared 

 from fresh material, the internode being held in pith or carrot ; but 

 better results will be obtained by treating first with acetic acid 

 to dissolve the lime which is often present in large quantities : 

 then after hardening in alcohol the stem may be embedded in 

 paraffin, and transverse sections be cut. The sections will show 

 a large circular central cell, surrounded by a single layer of 

 smaller cells of the cortex. 



2. The leaves, which are also covered in their basal 

 part with cortex, but the cells are straight or only 

 slightly curved. Note that the nodes of the leaves may 

 be seen to be marked by cells which project as round 

 bosses (leaflets), or in some species they are elongated. 

 The single cells of the cortex of the leaf extend half way 

 between two successive nodes and at the middle of the 

 internode, the cells meet end to end, the ends of those 

 descending from the upper node alternating with those 



