XV.] THE BRACKEN FERN. 455 



section but longer; the protophloem cells, 

 elongated, with thickened walls ; the cells of 

 the bast parenchyma somewhat elongated; 

 the relatively large sieve tubes, of great length 

 with oblique ends ; their lateral walls marked 

 by irregular groups of minute pores. 



fi. The vessels of the xylem: elongated tubes 

 presenting oblique perforated partitions, at 

 long intervals. Two forms of vessels will be 

 seen, viz. scalariform vessels, with regular 

 transverse thickenings on their walls and 

 smaller spiral vessels (protoxylem), less nume- 

 rous than the last form, with a continuous 

 spiral thickening on their walls. Among the 

 vessels the square-ended cells of the xylem- 

 parenchyma will be recognised. 



6. By macerating in Schulze's mixture (see Appendix E) 

 the various cells and vessels may be isolated one from 

 another, and their form better observed. 



7. By making a series of transverse sections from the 

 growing end of a stem the gradual development of the 

 various forms of tissue from the originally uniform 

 parenchyma (meristem] of the growing point, may be 

 traced. If a section through the actual apex be obtained 

 it will be possible to make out the relatively large, 

 wedge-shaped apical cell. 



c. The leaf. 



i. Hold a small piece of a barren leaflet in pith or imbed 

 it in paraffin and cut a thin vertical section at right 

 angles to one of the veins. 

 Observe with low and high power 



a. The epidermis of the upper and lower surface. 



