178 PRACTICAL BOTANY. 



are ranged side by side, the longer axes of the ellipses 

 being horizontal as the plant grows, and parallel to one 

 another : the masses of xylem may be irregularly 

 connected one with another towards the centre of 

 the stem. 



III. Before proceeding to the study of these several tissues in 

 detail, cut transverse sections from the young stem, at about one 

 eighth of an inch below the apex ; treat some of these with dilute 

 potash, others with Schulze's solution. Observe that in these 

 sections the tissues at the centre of the vascular cylinder are still 

 thin- walled, and have plentiful protoplasm, i.e., they are not fully 

 developed ; towards the periphery, however, will be seen a series 

 of groups of tissue showing the characters of developed xylem, 

 and alternating with these is a series of groups of phloem tissues. 

 Other preparations may be made successively from points further 

 from the apex, and from these the conclusion may be drawn that 

 the vascular tissues at the periphery of the vascular cylinder are 

 matured first, and that the development proceeds towards the 

 centre. (Compare roots.) 



IY. Returning to the sections of the old and mature 

 stem, examine the vascular tissues under a high power. 



i. Immediately within the so-called Bundle-sheath 

 is a band of tissue, which abuts directly upon the 

 periphery of the xylem and phloem, and having cell- 

 walls which stain blue with Schulze's solution; this may 

 be regarded as the Phloem-sheath. 



ii. On examining the masses of Xylem, observe 

 that 



a. The constituent elements are much smaller at the 

 periphery of the vascular cylinder than towards the 

 centre ; the former are the first developed or Proto- 

 xylem elements. 



&. The main constituents of the xylem are elements 

 with large cavity, and of rounded polygonal form 



