THE SPERMAPHYTES. 215 



outer side of the cambium layer. Which are the more 

 abrupt ? 



Examine the cells of the cortical parenchyma. What is 

 their prevailing shape ? Do you find intercellular spaces ? 



Consider the resin ducts. The study of the develop- 

 ment of young shoots shows that the resin ducts are inter- 

 cellular spaces which have arisen by the gradual drawing 

 apart of the cells to make room for the resin as it is se- 

 creted. Examine the cells of the two inner rows of glan- 

 dular cells next to the duct. In these cells the resin was 

 secreted. What is the shape of these cells ? Examine 

 the rows of cells next outside. In these cells starch was 

 stored up to be changed into resin by the action of the 

 cells of the two inner rows. Draw a resin duct with its 

 glandular cells under suitable power. 



Examine the cells of the cork layer. What is their 

 shape ? Draw a few. In this layer, cell division goes on 

 to a limited extent. 



Study the xylem under high power. The cells here 

 seen in cross section are known as trache'ides of the wood. 

 Draw a few. Find places where three separate layers 

 may be made out in the cell wall. Draw. Find on the 

 radial walls places where the layers have separated and 

 present somewhat the appearance of a double-convex lens 

 seen in section. These are sections through bordered pits. 



Trace a medullary ray from the pith parenchyma out 

 into the cortical parenchyma. Those that can be so traced 

 were the first to originate, and are called primary medul- 

 lary rays. There are others that extend only part way 

 from the pith to the cortex ; these formed later and are 

 called secondary medullary rays. The medullary rays 

 originate in the crowding together of the older cells by 

 the rapidly forming new cells of the cambium. 



Examine a resin duct in the xylem and compare its 

 structure with the resin ducts of the cortex. Draw. 



