156 THE MICROSCOPIST. 



ticed in connection with the axis or stem, the leaves, 

 flowers, and fruit. 



1. The Stem. The arrangement of fibro- vascular bun- 

 dles, i. e.. woody fibres and ducts, differs widely in the 

 two botanical divisions of Monocotyledons and Dicotyle- 

 dons. In the first the growth is endogenous, and a section 

 exhibits the bundles of fibres and ducts disposed without 

 regularity in the mass of cellular tissue which forms the 

 basis of the fabric. In the second, or exogenous stems, 

 the fibro- vascular bundles are wedge-shaped, and inter- 

 posed between the bark and the pith, being kept apart by 

 plates of cellular tissue, called medullary rays, proceeding 

 from the pith. 



The course of the vascular bundles in monocotyledons 

 should be carefully followed, either by maceration or 

 minute dissection. In the dicotyledonous stem, sections 

 must be made in three directions, transversely, longitu- 

 dinally across the diameter, and at a tangent from the 

 bundles of fibres. The section-cutter, described page 63, 

 will be serviceable, although a sharp razor or scalpel may 

 serve. The size, form, and contents of the pith-cells 

 should be noticed, and their transition to wood-cells. 

 The arrangement of the medullary rays, of the wood-cells, 

 and of the ducts must also be observed, and in the Coni- 

 ferse the position of the pits. The cambium layer, between 

 the bark and wood, may have its cells rendered more 

 transparent by weak alkalies, and their contents tested 

 with iodine -solution. The course and construction of 

 laticiferous vessels in the bark, when present, and of the 

 cork-cells of the tuberous layer, may be noted. 



Fossil woods may be cut with a watch-spring saw, and 

 ground on a hone like bone or teeth. Sometimes it is 

 best to break off small lamella by careful strokes with a 

 steel hammer. It is sometimes useful to digest fossil 

 wood in a solution of carbonate of soda for several days 

 before cutting. 



