152 PRACTICAL BOTANY 



under a low power, using a high power when necessary, and 

 observe the following tissues in succession, starting from the 

 periphery of the section : 



1. At the periphery a layer of small, thick-walled cells, 

 forming an ill-defined epidermis, with no stomata : it is covered 

 externally by a continuous cuticle. Beneath the epidermis, and 

 not clearly marked off from it, is 



2. The cortical tissue : the cells of the peripheral part of it 

 have thick stratified and lignified walls, with no intercellular 

 spaces. Passing inwards there is seen a gradual decrease in 

 thickness of the walls, and increase in size of the cells, till an 

 abrupt limit is reached at 



3. The lacunar tissue, consisting of thin-walled cells, which 

 form irregular trabecuise traversing the intercellular cavity 

 in a radial direction : this tissue may be regarded as the 

 equivalent of the endodermis. 



4. By means of these trabeculae the single central vascular 

 bundle is suspended in the middle of the large air- cavity : the 

 bundle is of elliptical outline, as seen in the transverse section, 

 and is built upon the concentric type : it is composed of the 

 following tissues : 



a. The pericycle, an irregular band of comparatively large, 

 thin-walled cells, which completely surround the central tissues, 

 and abut externally on the intercellular cavity, and the 

 trabeculae. The cells of this layer, in common with all the 

 outer tissses, including the epidermis, may contain chlorophyll- 

 corpuscles. 



b. The phloem, recognised as a tissue with thin cellulose 

 walls, small cavities, and sparing protoplasmic contents : though 

 reduced in bulk at the poles of the elliptical bundle, it forms a 

 continuous band surrounding 



c. The central xylem, which appears as a spindle-shaped 

 mass of tissue when seen in transverse section, and consists of 

 elements with lignified walls, and no cell- contents. 



Small vascular bundles of rounded outline, as seen in the 

 transverse section, may be found opposite or near to the ends 

 of the spindle-like vascular bundle ; these are bundles of the 

 leaf-trace cut through on their course inwards from the leaves : 



