HISTOLOGY OF THE lilllZOME. 117 



MINUTE ANATOMY OF THE RHIZOME OF PTKIUS AQUILINA. 



System. 



I. Epidermal 



Tissues. 



1. Epidermis. 



II. Funda- 

 mental, 



III. Fibro- 

 vascular. 



3. Fundamental 

 parenchyma. 



CHAUACTEUISTK.S. 



Cells polytronal in crftss-softion, cinijfv. Walls 

 hard, tliickened, especially towards the outsiil.- 

 (Fig. 49.) 



Cells rounded or poly^ronal in fross-sortion. color- 

 less. Thin-wallcd, coiitniiiinu prutopluMn, im. 

 ck'us and starch. Iiitercellulur spaces prescrn 



(Fig. 5:-', /.p.) 



•^olprntin Ttnr Cells polygonal or semi-fusiform in section, ncarlv 

 * tSumn empty. No interc-ellular spaces. Walls har-l 



cncnyma. ^^^ brown, thickened. (Fig. 49.) 



4. Sclerotic pios- 



enchyma (or Cells fusiform, empty. "Walls thick, red. (Fig. 5(1. i 

 sclerenchyma) 



5. Wood - par en 

 chyma. 



Like the fundamental parenchyma, but with more 

 elongated cells. (Figs. 52, .53.) 



6. Phloem-paren- 

 chyma. 



7. Phloem-prosen- 

 chyma, or 

 bast-fihres. 



8. Sieve-tubes. 



9. Tracheids (lad- 

 der-cells). 



10. Trachece or ves- 

 sels (spiral). 



Precisely like 5, differing only in position. 



Cells fusiform, rich in protoplasm, colorless. Walls 

 thick, soft. (Figs. 52, 53.) 



Having the ordinary characters (see preceding 

 table). (Figs. 52-5t.) 



Pits transversely elongated (scalariform). (Figs. 

 53-53.) 



Very slender, with one or two internal spiral thick- 

 enings. (Fig. 53.) 



Besides the above-mentioned tissues, the rliizonie contains 

 certain other secondary varieties whicli will be descri])cd further 

 on. 



Epidermal System. Epidermis. It is the fuiu'tiou <>f the 

 epidermis (aided in this case by the underlying sclerotic ])arc'n- 

 chyma) to protect the inner tissues from contact with thi' soil 

 and to guard against desiccation of the rhizome during ch-oiights. 

 The cells (Fig. 49) are dead and empty, with enormously thick, 

 hard walls perforated by numerous branching canals. The outer 

 wall is especially thick. 



Fundamental System. The tissues of this system form the 

 main body of the plant, and in the fern have two widely ditTcr- 



