192 PRACTICAL BOTANY. 



they are embedded in the ground-tissue, and are 

 sharply circumscribed by a narrow, light brown layer 

 of cells without intercellular spaces : this is the Bundle- 

 sheath. Among the tissues inclosed by this sheath, 

 note that a large central mass may be distinguished as 

 consisting for the most part of elements with large 

 cavity, no cell-contents, and rather thick walls with a 

 peculiar marking : this is the Xylem * Between this 

 and the bundle- sheath is a broad band of tissue with 

 thin, bright-looking walls, and with protoplasmic con- 

 tents : this is the Phloem. Since the xylem is sur- 

 rounded by the phloem, this bundle is said to be of the 

 concentric type. 



In the sections treated with Schulze's solution, note 

 that the walls of the inner ground-tissue stain blue, 

 and that starch is found in the cells : that the bundle- 

 sheath appears browner than before, that the walls of 

 the phloem stain blue (cellulose), and the contents 

 yellowish : that the walls of the chief constituents of 

 the xylem stain yellow (lignified). In the sections 

 treated with acid aniline sulphate observe the yellow 

 coloration of the walls in the xylem, while those of the 

 phloem are not stained. 



VII. As the vascular bundles of the leaf -stalk are 

 better fitted for minute observation, and are better types 

 of the concentric bundle of the Fern than those of the 

 stem, cut thin transverse sections of the lower part of 

 the petiole. Having previously noted with a low power 

 that in their main features the tissues resemble those 

 above observed in the stem, examine the structure of 

 one vascular bundle under a high power, and starting 

 from the periphery of it note successively 



