BIOLOGY OF HIGHER SEED PLANTS 43 



years marked? What is the relative width and 

 texture of spring and summer wood.? 



b. Observe the number and extent of the wood rays ; do 



they all extend to the pith? What is their outer 

 terminus ? 



c. The pith. Observe its size and shape. 



d. Do some of your blocks show central heartwood and 



outer sapwood ? Compare two or three different kinds 

 of woods as regards the above points, if specimens 

 are available. 



LONGITUDINAL SECTIONS 



1. Compare longitudinal sections of branches, cut in both 

 radial and tangential planes, with the above transverse 

 sections. For this purpose it is preferable to use oak 

 blocks which present for comparison transverse, longi- 

 tudinal radial, and longitudinal tangential cut surfaces. 

 a. Compare as follows the different surfaces of wood blocks 

 prepared as indicated above : 



(1) Determine the transverse, radial, and tangential 



surfaces of a wood block. Locate corresponding 

 structures in each ; namely, wood rays, annual 

 rings of growth, spring and summer wood, and 

 heartwood and sapwood if present. 



(2) What are the distinctive features of radial and 



tangential cuts which enable you to distinguish 

 them ? In a tangential section, is a wood ray 

 cut across its long axis or parallel with it ? In 

 a radial section ? What is the actual form of a 

 wood ray in a tree trunk ? 



(3) Drawings. Make accurate sketches of the three 



surfaces of a wood block to show the wood rays, 



