THE SPERMAPHYTES. 



229 



stem. Draw and locate all the tissues shown in Fig. 146. 

 Under high power examine the vessels of the xylem for 

 markings on the walls. Scalariform vessels, i.e., vessels 

 whose side walls are so marked as to resemble ladders ; 

 spiral vessels, i.e., vessels with a band running about 

 them spirally; annular vessels, i.e., vessels with rings of 

 thickened tissue at intervals; and pitted vessels may be 

 found in favora- 

 ble sections. In 

 the region of 

 the phloem, bast 

 fibers are found, 

 i.e., elongated, 

 narrow vessels 

 with pointed 

 ends ; also sieve 

 tubes, i.e., tubes 

 with more or 

 less circular 

 plates on their 

 surfaces which 

 serve as sieves 

 to allow the pas- 

 sage of certain Af 



portions of the FIG. 148. Transverse section of mature Grape stem, 

 protoplasm from showing a number of annual layers, large and 

 small vessels, and medullary rays. (X 35.) 



cell to cell. It 



may not be easy to make these out. Treat pieces of the 

 stem with Schultze's macerating mixture, dissect them, 

 and search for all the above vessels. 



5. Cut a transverse section of the Milkweed stem. 

 Draw it under low power and label all the parts you 

 can make out by comparing it with Fig. 146. It will be 

 seen that this stem corresponds very well with the Gera- 

 nium stem in structure. There is a tendency to divide 



