PERN AXLIBS OF NEW ZEALAND. 19 



There are 4 genera and 14 species of the order in these islands. 



Order VI. — Isoeteae. This is a small order, consisting of a single 

 genus (Isoetes), which is included among Lycopods by many 

 botanists. Though nearly allied to them, it has some very distinctive 

 characters, which mark it at once. Most of the plants forming it 

 are aquatic and submerged, living at the bottom of pools and 

 lakes; a few are terrestrial. The leaves or fronds are grass-like, and 

 have a well-developed sheath. This is hollowed out at the base into 

 a pouch, which is surrounded by a narrow border, and has a scale or 

 ligule above it. The pouch encloses a membranous sac, the 

 sporangium, which is divided by transverse partitions into several 

 ■compartments. All the sporangia appear externally similar, but 

 those of the outer leaves are macro-sporangia, containing from 40 to 

 200 macrospores, while those of the inner leaves are micro-sporangia, 

 and contain a vast number (probably over a million) of flour-like 

 microspores. The prothallus develops from the former, while it is 

 still ripening. 



Two species of Isoetes have been found in our lakes. 



The only remaining group of the Vascular Cryptogams not yet 

 mentioned is that of the Equisetacece or Horse-tails. These plants 

 are tolerably familiar to all who have collected botanical specimens 

 in England, but are not found at all in New Zealand ; in fact, they 

 are absent throughout nearly the whole of the Southern hemisphera 



