LYCOPODIUM SPOROPHYTE 279 



b. The main constituents of the xylem are elements 

 with large cavity, and of rounded polygonal form 

 (tracheides) : note the structure of the wall, especially 

 where two of these adjoin one another. 



iii. In the phloem there will be found at the 

 periphery of the vascular cylinder, and alternating 

 between the successive groups of protoxylem, masses of 

 tissue with thick cellulose walls, and small cell-cavities : 

 these are the protophloem groups, or first-formed 

 elements of the phloem. Passing from these towards 

 the centre of the vascular cylinder, the phloem is found 

 to consist of 



a. Constituents with large cavities, and very scanty 

 cell-contents. 



b. Elements with small cavity, and obvious cell- 

 contents. 



V. Cut radial longitudinal sections through a mature 

 stem : mount as before, examine them first with a low 

 power and note 



1. The bases of the leaves continuous with the 

 epidermis and cortex of the stem. 



2. The cortex showing the same differentiation into 

 successive bands (a), (b), (c), as was seen in the trans- 

 verse section. 



3. The central vascular cylinder. 



4. Small vascular bundles of the leaf-trace, 

 which may be seen pursuing an oblique downward 

 course from the bases of the leaves, through the cortex, 

 to the periphery of the vascular cylinder : since these 

 bundles may be followed in one radial section from the 

 leaf to the central cylinder, it follows that that part of 

 their course is approximately in a radial plane. 



