INTRODUCTION TO CRYPTOGAMIC BOTANY. 5 IS 



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vascular bundles, forming a sort of balloon as they proceed 

 from a common base below, and then converge to the apex. 

 Oleandra neriiformis is remarkable for its erect shrubby 

 rhizoma, which rises to a height of from four to six feet, and 

 bears whorls of fronds ; it grows in open spots. 



619. The second section is familiar, as far as the name goes, 

 to every lover of Ferns, though the gf^nus Aspidium, as now 

 limited, is confined to a few tropical species, with compound 

 anastomosing veinlets, producing free veinlets in various direc- 

 tions. Sagenia differs principally in the absence of the 

 latter. Polystichum contains species with free veinlets, and 

 a peltate indusium. Cyrtomium has medial sori, the lower 

 veinlet free, and the upper anastomosing, and producing free 

 veinlets on their outer sides and angular junctions. Phanero- 

 iMebia differs from this merely in more of the veinlets being 

 free. Fadyenia has reticulate and anastomosing veinlets, and 

 apical biseriate sori. MesoMcena or Sphcerostephanos is dis- 

 tinguished from Nephrodiumi by the linear sori. The glan- 

 dular margin of the indusium occurs also in some species of 

 Nephrodiuim. Pleocnemia differs from Sagenia principally 

 in the gigantic habit. Didymochlcena requires especial 

 notice, on account of its oblong elliptic sori and indusia, fixed 

 to the frond by a longitudinal crest ; an exaggeration of the 

 usual reniform indusium. It is also said to be arboreous ; 

 but old plants of D. sinuosa, a Brazilian species, exist in the 

 Kew Garden, which have not assumed the habit of a tree 

 fern. Matonia, referred formerly to Cyatheacew, appears 

 more properly to be placed here, on account of its superior 

 indusium, which covers only a definite number of sporangia, 

 thereby showing a strong analogy with Oleichenia. The 

 stout rhizoma is said to be creeping, though six or eight feet 

 long. Most of the genera are tropical ; but Lastrea, Nephro- 

 diwm, and Polystichum have numerous European species, or 

 species which belong to temperate regions. These are often 

 extremely variable, nor can the same reproach be withheld 

 from many tropical species. 



15. Peranemace^, Presl. 



Sori globose, pedunculate, or seated on the middle of the 



