94 FILICALS. [BOOK i. 



very general statement. The trunk is covered with a hard 

 rind, occupying the place of bark, two or three lines thick, 

 and consisting of hard brown parenchymatous and prosen- 

 chymatous tissue, the latter, if present, being on the inside. 

 Within the rind is a mass of parenchymatous thinner-sided 

 tissue, which is analogous to the horizontal cellular system of 

 exogens and endogens. The wood is formed by concave or 

 sinuous plates, whose section has a lunate or wavy form, and 

 which are closely arranged in a circle next to the rind, en- 

 closing a column of parenchyma, just as the wedges of wood 

 in exogens enclose a similar column of pith ; and in like 

 manner there are openings between the plates, through which 

 the subcortical and medullary parenchymas communicate. 

 Each plate consists externally of several layers of hard brown 

 prosenchyma, next within which is a pale stratum of thin- 

 sided parenchyma, and in the centre of all is a soft pale mass 

 of trachenchyma, consisting of large scalariform and spiral 

 vessels (sometimes - line in diameter) mixed with soft 

 parenchyma. Externally the stem is marked with long, or 

 rhomboidal scars, .the surface of which is broken into nume- 

 rous hard ragged projections which represent the broken 

 communication between the trunk and the leaves, by the fall 

 of which the scars are produced. Next the apex of a trunk 

 the scars are always arranged with great regularity, but 

 towards the lower part of the stem they become much longer, 

 irregular in form, and are separated by deep furrows ; from 

 which it is to be inferred, that, although in these plants no 

 new parts are added, except at the point of the trunk, yet 

 that the parts after being formed do grow both in length and 

 breadth. 



Below the scars of the leaves are often (always ?) found 

 elliptical or roundish perforations, filled with a powdery 

 matter. These have no obvious analogy in other plants, 

 unless they are to be compared to the perforations in the 

 rhizome of Nymphsea, which, however, according to Trecul, 

 are caused in that plant, by the falling away of roots. (See 

 last volume.) 



Their petioles, or stipes (rachis W. j peridroma, Necker), 

 consists of sinuous strata of indurated, very compact tissue, 



