84 PRACTICAL BOTANY 



Horse-Chestnut. In longitudinal sections through the base of a 

 leaf, which is almost ready to fall, note that the brown band of 

 cork on the stem stops short at the base of the leaf, and that 

 close to the point where it stops is the starting-point for the 

 similar corky layer which runs directly across the base of the 

 petiole, cutting the vascular bundles at right angles, and con- 

 tinuous through them. 



Examine such a section under a high power, and note 



1. The radial rows of cork-cells, with the phellogen on the 

 side next the stem. 



2. A band of cells outside the cork, which are of yellowish 

 colour, and the individual cells are rounded, having large 

 intercellular spaces between them ; thus this layer, which has 

 been styled the abciss layer, is easily ruptured. 



3. The cells of the tissues of the leaf are almost empty with 

 the exception of crystals : those of the stem, below the layer 

 of cork, have plentiful protoplasm, and starch. 



Comparisons may also be made of similar material of the 

 Poplar, Ash, or Walnut, which are well adapted for illustrating 

 the process of defoliation. 



