FERN ALLIES OP NEW ZEALAND. » 



covered by a 2-valved involucre, the lips of -which open outwards 

 (PI. I. fig. 76). This prolongation of the veins is termed the 

 receptacle ; in the true filmy-ferns it occasionally protrudes beyond 

 the lips of the involucre, when it is said to be exserted. In Loxsoma 

 (PI. I. fig. 6a) and in Triclwmanes (PI. I. fig. 8fls) this receptacle is 

 usually very considerably exserted, and the involucre is still further 

 modified into a long narrow tube or cup. 



In Adiantum (Maidenhair) (PI. II. fig. 3), Hyiwlepis (PL II. fig. 

 4), Lomaria, and many other genera, the involucre is often termed a 

 false one, being the result simply of the margin of the frond being 

 turned or rolled back over the sorus. One of the most anomalous 

 forms is to be found in Marattia, in which the capsules are united 

 into boat-shaped groups, called Synangia (PL IV. fig. 2a). Until 

 the development of these peculiar sori has been fully investigated, 

 we cannot decide how they are formed nor what relation they hold 

 to the sori of other families of ferns. So different are they in 

 structure and development that Sachs considers that the whole 

 family to which this genus belongs should be removed from the true 

 ferns, and classed, together with the Ophioglossacese and Equisetaceae 

 (horse-tails), in a separate group or order by themselves. 



The only other point we need to note here in regard to the 

 external form of ferns is the shape and structure of the capsule 

 {sporangium) itself, and the position of the ring. The former is 

 formed of a single layer of cells arising from the outer skin or 

 epidermis of the frond, and the ring is a layer of the same group of 

 cells somewhat modified in form. The capsules vary in form, some 

 being globular (Gleichenia, PL I. fig. la), others pear-shaped (Poly- 

 podium, &c.) ; but it is the position of the riug which is the most 

 marked feature in them. This constitutes, in fact, the most distinc- 

 tive character by which the tribes of ferns are separated from one 

 another ; but as it is detailed in full in Chap. III., it is not necessary 

 to go into much explanation of it here. It is worth noting, how- 

 ever, that when the annulus is transverse (as in Gleiclienia) or 

 oblique {Cyathea), or when it forms a cap on the top {Schizoea), then 

 the opening or dehiscence of the capsule is necessarily longitudinal ; 

 while, if the ring is vertical, passing over the top of the capsule, the 

 dehiscence is transverse. This is found in all the tribe of the Poly- 

 podiacese, to which by far the largest number of our ferns belong. 



