144 



PRACTICAL BOTANY 



the surface of the scar : mount in glycerine, and observe 

 below the scar the tissues as above described for the 

 stem (p. 88 &c.). At the level of the scar the following 

 structural points are to be noted : 



1. The rough and irregular outer limit of the tissues, 

 with dried up remains of cells often projecting beyond 

 the general surface. 



2. The dark brown band of cork, without inter- 

 cellular spaces, which covers the scar, and protects the 

 internal tissues. 



3. The projecting end of the vascular bundle : mark 

 especially how the corky formation is continuous into 

 the tissues of the bundle, evidently having there arisen 

 from the division of cells of the parenchyma of the 

 bundle : also note that the vessels of the xylem are 

 laterally compressed by the adjoining cells, and their 

 broken ends are thus closed at the surface of the 

 scar. 



Sections should also be made from material taken 

 in autumn just at the period of the fall of the leaf, so 

 as to see the changes in the tissues at the base of the 

 petiole which precede the rupture. These may be 

 particularly well seen in the 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 continuous through them. 



Examine such a section under a high power, and 

 note 



