HISTOLOGY OF THE RHIZOME. 



117 



MINUTE ANATOMY OF THE RHIZOME OF PTERIS AQUILIXA. 



SYSTEM. 



TISSUES. 



CHARACTERISTICS. 



I. Epidermal 



1. Epidermis. 



Cells polygonal in cross-section, empty. Walls 

 hard, thickened, especially towards the outside. 

 (Fig. 49.) 



2. Fundamoitol 

 parenchyma. 



Cells rounded or polygonal in cross-section, color- 

 less. Thin-walled, containing protoplasm, nu- 

 cleus and starch. Intercellular spaces present. 

 (Fig. 52, /.p.) 



II. Funda- 

 mental. 



enchyma. 



. . Cells polygonal or semi-fusiform in section, nearly 



empty. No intercellular spaces. Walls hard 

 and brown, thickened. (Fig. 49.) 



4. Sclerotic pn/ 



enclnjma for Cells fusiform, empty. Walls thick, red. (Fig. 50.) 

 sclerench yma) 



5. Wood - paren - 

 city ma. 



Like the fundamental parenchyma, but with more 

 elongated cells. (Figs. 52, 53.) 



6 ' 



III. Fibro- 

 vascular. 



7. PJiloem-prosen- 

 e/ij/wa, or 

 bast-fibres. 



8. Sieve-tubes. 



9. Tracheids (lad- 

 der-cells^. 



10. Tracheae or ves- 

 sels (spiral). 



Precisel y 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. 52-54.) 



Pits transversely elongated (scalariform). (Figs. 

 52-53.) 



Very slender, with one or two internal spiral thick- 

 enings. (Fig. 52.) 



Besides the above-mentioned tissues, the rhizome contains 

 certain other secondary varieties which will be described further 

 on. 



Epidermal System. Epidermis. It is the function of the 

 epidermis (aided in this case by the underlying eclerotic paren- 

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

 and to guard against desiccation of the rhizome during droughts, 



~ ~ o ~ 



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 differ- 



