^X] RECENT FERNS 309 



moorland carpeted with Pteris aquilina afford an example of the 

 monopolisation of the soil by a single species. In Sikkim Sir 

 Joseph Hooker speaks of extensive groves of tree ferns, and in 

 the wet regions of the Amazon, Bates ^ describes the whole 

 forest glade as forming a " vast fernery." In a valley in Tahiti 

 Alsophila tahitiensis is said to form "a sort of forest almost to 

 the exclusion of other ferns I" In the abundance of Glossopteris 

 (figs. 334, etc.) fronds spread over wide areas of Permo- 

 Carboniferous rocks in S. Africa, Australia, and India, we have 

 a striking instance of a similar social habit in an extinct fern 

 or at least fern-like plant. 



Acrostichum aureum, with pinnate fronds several feet long, 

 is an example of a recent fern covering immense tracts, but this 

 species^ is more especially interesting as a member of the 

 Filicineae characteristic of brackish marshes and the banks of 

 tropical rivers in company with Mangrove plants and the 

 " Stemless Palm " Nipa. This species exhibits the anatomical 

 characters of a water-plant and affords an interesting parallel 

 with some Palaeozoic ferns (species of Psaronius) which probably 

 grew under similar conditions. 



The Anatomy of Perns. 



The text-book accounts of fern-anatomy convey a very in- 

 adequate idea of the architectural characters displayed by the 

 vascular systems of recent genera. When we are concerned 

 with the study of extinct plants it is essential to be familiar not 

 only with the commoner recent types, but particularly with 

 exceptional or aberrant types. The vascular system of many 

 ferns consists of strands of xylem composed of scalariform 

 tracheae associated with a larger or smaller amount of paren- 

 chjona, surrounded either wholly or in part (that is concentric 

 or bicoUateral) by phloem : beyond this is a pericycle, one layer 

 or frequently several layers in breadth, limited externally by an 

 endodermis, which can usually be readily recognised. The vas- 

 cular strands are embedded in the ground-tissue of the stem 



1 Bates (63) A. p. 30. " Challenger Reports (85) p. 785. 



3 Tansley and Fritsch (05) p. 43 ; Thomas, B. N. (05). 



