58 



ISOETACEAE (QUILLWORT FAMILY) 



* * Leaves shorter above and below, stipule-like ; the lateral larger, 2-ranked. 



3. S. apus (L.) Spring. Stems tufted and prostrate, creeping, much 

 branched, flaccid ; leaves pellucid-membranaceous, the larger spreading hori- 

 zontally, ovate, oblique, mostly obtuse, the smaller appressed, taper-pointed ; 

 those of the short spikes nearly similar ; larger spore-cases copious at the lower 

 part of the spike. Low, shady places, s. Me. , south w. and westw. A delicate 

 little plant, resembling a Moss or Jungermannia. (S. A.) 



ISOETACEAE (QUILLWORT FAMILY) 

 (REVISED BY A. A. EATON.) 



Small aquatic or palustrine herbs of grass-like or rush-like aspect. Stem 

 short, thick, and corm-like, crowned with numerous subulate leaves. Spores of 

 two kinds in distinct axillary solitary sporangia. A single genus ; the species 

 similar in habit and to be distinguished with certainty only by the aid of the 

 compound microscope. 



1. IS6ETES L. QUILLWORT 



Stem fleshy, more or less depressed, the roots arising from the 2-5-lobed 

 base, the flattened top bearing the leaves from a central bud or crown. Leaves 

 dilated and imbricated at base, rounded or somewhat 

 angular above, orbicular in section, traversed by four 

 air-tubes that are separated by cross-partitions, bearing 

 a bast-bundle in the center and often 4 or more in the 

 periphery. Stomata none or in narrow 

 bands over the air-cavities. Sporangia 

 in excavations of the dilated bases of 

 the leaves (more or less covered by the 

 velum, formed from the thin edges of 

 the excavation) , attached by their backs, 

 orbicular to ovoid, plano-convex, trav- 

 ersed internally by transverse threads, 

 their thin integuments often bearing 

 small dark sclerenchymatous cells. 

 Spores dimorphous, the female or gyno- 



spores large (250-1000 /* or more in diameter), spherical, with 

 an elevated ridge (equator) around the middle and three others 

 (commissures) arising from this and meeting at the summit of 

 the upper hemisphere, the surface variously beset with siliceous 

 elevations, rarely smooth ; the male or androspores in separate 

 sporangia, mostly in alternate cycles with the female, very 

 minute (20-45 /* long), obliquely oblong, triangular in section. 

 The trunks of all our species but 7. Tuckermani and /. sac- 24. I. riparia, show- 

 charata, var. Amesii are habitually bilobed. (Name used by ing generic habit 

 Pliny, presumably for a house-leek.) FIGS. 23, 24. x %. 



1. Submersed ; leaves cylindrical, fleshy, without bast-bundles or stoinata. 



AQUATIC AE A. Br. a. 

 a. Leaves stout, rigid, erect. 



Gynospores honeycomb-reticulated below 1. I. macrottpora. 



Gynospores with distinct or anastomosing crests (1) 7. macrospora, v. heterospora. 



a. Leaves mostly slender and spirally spreading or recurved b. 

 b. Gynospores with thin jagged honeycomb-reticulated crests. 

 Leaves 1 mm. or less in diameter. 

 Leaves reddish or olive, often with a few stomata ; spores 600 /x 



or less in diameter 2. 7. Tuckermam. 



Leaves green, recurved at end, not spiral ; spores averaging 



650 ju, in diameter (2) 7. Tuckermani, \. borealis. 



Leaves 2.5-3 mm. in diameter .... (2) 7. Tuckermani, v. Harveyi. 



b. Gynospores with thick vermiform free or anastomosing ridges . .3.7. hieroglyphica, 

 2. Plants of inundated shores or tidal flats, fruiting as the water recedes ; 

 with stomata but no bast-bundles. AMPHIBIAE A. Br. c. 



..sponngium. 



23. Isoetes (diagrammatic). 

 Inner surface of leaf-base. 



