INTRODUCTION TO CRTPTOGAMIC BOTANY. 537 



Several species of Oheilanthes are beautifully farinose 

 underueath. Amongst many tropical and subtropical species 

 we have here many essentially temperate, and others which 

 have an extremely wide distribution, as Pteris aquilina, 

 which occurs variously modified in all parts of the world. 

 Nearly a fourth of the New Zealand ferns belong to this section. 



11. DiCKSONiACEvE, Presl. 



Sori globose, submarginal, seated at the tip of a vein or vein- 

 let ; indusium lateral, persistent, bivalvate, the lower valve 

 formed by the true indusium, the upper by the altered tooth 

 of the frond folded back. Often arboreous. 



610. This tribe is allied to Gystopterideos, as regards the 

 true indusium, and to AdiantiacecB, so far as the margin of 

 the frond conduces to the formation of the indusium. In 

 Balantium, the indusium forms a cup, to which the false indu- 

 sium makes a sort of lid. Gihotiwm is distinguished by its 

 nearly equal valves, whereas in Dicksonia they are unequal. 

 Leptopleuria has a coriaceous true indusium placed at the 

 very margin. It differs principally from Dicksonia in all the 

 parallel veins being fertile, and not a select few only. Patania 

 has a saucer-shaped indusium, covering only the base of the 

 sorus, the true and false indusia being completely connate. 

 CystodiuTn is remarkable for the cuculliform false indusium, 

 the margins of which are connivent, while the true indusium 

 is plane. Sitolobium differs from Dicksonia in its creeping 

 rhizoma and delicate texture. Thyrsopteris has semiglobose 

 sori, with coriaceous cupshaped indusia, disposed in a panicu- 

 late thyrsus. The fertile frond is, in fact, reduced to a mere 

 rachis, like TrichomaTies pluina, Hook. The sterile fronds 

 have simple or forked veins in the same disc. It forms a 

 slender caudex. Deparia is a Thyrsopteris with the paren- 

 chymatous border developed, so that the cups are marginal, 

 after the fashion of the inflorescence of some Xylophylla. 

 This tribe contains some of the finest of the tree ferns. Dick- 

 sonia antarctica has a uniform girth of 12 feet, through 

 its height of 40. Dicksonia squarrosa reaches the farthest 

 south of all the tree ferns. Dicksonia lanata sometimes forms 

 a distinct caudex, but not always. In fact, tree ferns in gene- 



