1042 LYCOPODIACER. [Psilotum. 
Fil. t. 87; Fil. Exot. t. 63; Hook. f. Fl. Nov. Zel. i. 56; 
Handb. N.Z. Fl. 391; Benth. Fl. Austral. vii. 681; Bak. Fern 
Allies, 30; Thoms. N.Z. Ferns, 108. P. heterocarpum, Col. im 
Trans. N.Z. Inst. xx. (1888) 237. 
Kermabec Isuanp: Not uncommon, 7. F. C. Norru Istanp: Rangaunu 
Harbour, R. H. Matthews! Rangitoto Island, Colenso! and many others ; 
Auckland Isthmus, very rare, T. Ff. C.; Motuhora Island (Bay of Plenty), 
Joliffe; near Maketu, Kirk; soil heated by hot springs at Orakeikorako, 
Rirk! Wairakei, C. J. Norton! and Tokaanu, T. F. C. Sea-level to 
1800 ft. 
In all tropical and subtropical regions as far north as Japan and Florida. 
Orper XCVII. _ISOETACEA:. 
Aquatic or amphibious perennials, often entirely submerged, 
rarely terrestrial. Stem (corm) short and tuberous, of firm texture, 
2-3-lobed ; roots numerous, rather fleshy, dichotomously forked, 
springing from the furrows of the stem. Leaves many, forming a 
dense tuft at the top of the stem, linear or filiform, flat in front, 
rounded at the back, dilated and sheathing at the base, always 
furnished with 4 longitudinal air-channels divided by transverse 
partitions, and with a single central vascular bundle; stomata 
present, or absent in those species which are permanently sub- 
merged. Sporangia large, membranous, placed in a hollow (fovea) 
of the dilated base of the leaf and sometimes partly concealed by 
the membranous margin (velum or indusium) of the fovea, 1-celled, 
but often imperfectly divided by rods or plates of tissue (trabecule), 
those of the outer leaves containing macrospores, those of the inner 
leaves microspores. Immediately above the fovea is a flattened 
membranous plate called the ligule. Macrospores large, globose, 
usually chalky-white, with three ribs radiating from the apex. 
Microspores very minute, trigonous. 
A very isolated family, consisting of the single genus Isoetes, allied on the 
one hand to the Lycopods and on the other to ferns. In germination a male 
prothallium with a single antheridium containing spermatozoids is developed 
within the microspore, the spermatozoids being set free by the bursting of the 
coats of the microspores. The macrospores in a similar manner each produce a 
female prothallium bearing 2 or 3 archegonia, which are ultimately exposed by 
the splitting of the macrospore along the three ridges. Fertilisation then takes 
place in the same way as in ferns. 
1. ISOETES, Linn. 
Characters of the order. 
Widely distributed in most temperate and tropical regions. Over 60 species 
are admitted in the most recent enumeration, but many of them are very im- 
perfectly known. The two found in New Zealand are endemic. 
Macrospores tubercled <- 5 es = ayer aaa 
Macrospores smooth .. os 5 os .. 2, I. alpinus. 
