POLYTRICHUM OOPHYTE GENERATION 345 



serrated margin : the basal portion of the leaf, which is 

 closely applied to the stem, is broad, but thin and 

 membranous, and is not marked by longitudinal 

 strise. 



V. Cut transverse sections of leaves : this may easily 

 be done by holding the terminal bud of a mature plant 

 between pieces of pith, or by embedding in paraffin, 

 and then cutting transverse sections of the whole bud. 

 Mount all the sections as before, and examine first with 

 a low power. Neglecting the almost circular transverse 

 sections of the stem, recognize 



1. Those transverse sections which have passed 

 through the sheathing basal portions of the leaves : 

 these may be readily distinguished by their broad 

 lateral wings, only one layer of cells in thickness. 



2. Those which have been taken from the upper 

 part of the leaf: these maybe distinguished by their 

 more bulky appearance. 



Having recognized these sections, put on a high 

 power and examine them in detail : 



1. In the section of the sheathing base of the leaf 

 observe 



a. The two lateral wings, consisting of a single layer 

 of cells, with thickened outer walls, and but little 

 chlorophyll. 



b. The more bulky central portion consisting of 



i. An irregular layer of superficial cells with thickened 

 outer walls, covering both upper and lower surface : 

 beneath these are 



ii. Bands of sclerenchyma, in which the lumen is 

 almost obliterated. 



iii. Within these lies a " vascular bundle " consisting 



