PINUS. STEM. 139 



a. Separated from one another laterally by bands of 

 parenchyma. 



b. Their form is approximately wedge-shaped. 



c. That the tissues of which they are composed may 

 be distinguished as 



i. A Xylem portion, nearer the centre of the stem, 

 the components of which have thick, dark-looking, 

 lignified walls (yellow with Schulze's solution). These 

 first formed xylem elements, since they differ from 

 those formed later, are distinguished as Protoxylem. 



ii. A Phloem portion, nearer the periphery, with 

 bright-looking cellulose walls (blue with Schulze's 

 solution). 



The more minute study of these tissues must be 

 deferred for the present. Outside the ring of vascular 

 bundles is 



3. The Cortical tissue, a mass of cells similar in 

 structure to the pith. In this occur large intercellular 

 spaces, which are Resin-passages. Since the periphery 

 of the section of the axis of the bud is complicated by 

 great irregularity of outline, the study of the outer 

 tissues will be better carried out in the older stem. 



II. Cut transverse sections of the stem of the current 

 year. Mount some in glycerine, others in Schulze's 

 solution. The sections have a wavy outline, the in- 

 dentations corresponding to the grooves above observed 

 externally. Starting from the periphery of the section, 

 note the following tissues : 



1. Epidermis, a single layer of cells, following the 

 wavy outline of the section : the walls, especially the 

 outer, much thickened : externally a Cuticle. 



2. Cortical tissue, consisting of cells with rather 



