POLYPODIUM VULGARE 75 



plasm, has disappeared, leaving only the 

 cell-walls, unevenly thickened. In some 

 plants (e.g., the pine) the thickenings form 

 " bordered pits." 



(9) Smaller sieve-tubes, resembling those of 

 the phloem. 



(10) Thin- walled cells forming the wood-, or 

 xylem-parenchyma. 



(n) Since the tissues of the fibro- vascular 

 bundles are arranged circularly about a 

 common center, the bundle is called a 

 concentric bundle. 



(12) Compare the various bundles and see if 

 they are all of similar structure. 



(13) Make a careful drawing showing the 

 structure of the bundle, including all points' 

 mentioned under (g), (i)-(io). This draw- 

 ing should be at least 75 mm. in longest 

 diameter. 



2. The pinna. 



(a) Under the low power examine a small portion of 

 one of the pinnae or pinnules not bearing a 

 sorus, and note the presence or absence of 

 outgrowths. 



(b) Can you observe any veins too small to be seen 

 with the naked eye? If so, describe their re- 

 lation to each other. 



(c) Mount a small bit of the lower epidermis, and 

 describe (a) any outgrowths; (b) the stomata 

 and guard-cells, stating the number, shape, 

 and contents of the latter. Describe the rela- 

 tive number and distribution of the stomata. 



(d) Compare the stomata of the fermwith those of 

 a seed-bearing plant. 



