CHARACE^E 211 



2. The " leaves " or branches of limited growth, which are 

 arranged in whorls, the point of insertion of each whorl being 

 recognized as a node : the number in each whorl may vary. 

 Examine the leaves with a lens, and observe that they also 

 show a distinction of nodes and internodes ; in some species 

 whorls of small unicellular outgrowths (leaflets) may be seen at 

 the nodes : thus the leaves repeat the characters of the axis 

 on a smaller scale. 



3. In the axil of one leaf in each whorl is usually found a 

 branch of unlimited growth, which repeats all the characters 

 of the main axis. 



4. Examine the base of the plant where it is fixed in the 

 mud : very long transparent rhizoids may be seen to be 

 inserted at the nodes. 



5. On the inner side of the leaves of plants taken in summer 

 or autumn the sexual organs will be found, viz., the antheridia, 

 which are globular and of a red colour, and the oogonia, which 

 are of a dark olive colour or brown : these sexual organs are 

 seated, in the monoecious species, in pairs, at the nodes of the 

 leaves, and on the inner, adaxial, side of them. 



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 

 interne dai cell. Note that the cortex is composed of (a) 

 elongated cells, and (b) short cells which project as hemi- 

 spherical bosses, the whole being disposed in spirally curved 

 rows. 



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 cortex stops short below the 

 apex of the leaf, which is accordingly terminated by a series of 

 naked cells. 



3. Follow the leaves down to their base of insertion at the 

 node, and observe a series of short cells which project more 



P 2 



