42 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Sporangia associated in definite clusters (sori) on the under side or at the 

 margins of ordinary leaves, or within the hard, contracted divisions of 

 wholly fertile, greatly modified leaves, long-stalked, with a nearly 

 complete vertical ring, rupturing transversely, 



POLYPODIACEAE (p. 53). 



Sporangia covering thickly some or all pinnae of the fertile fronds, replacing 

 the ordinary leaf tissue, short-stalked, with a rudimentary apical ring, 

 opening by a longitudinal slit OSMTJNDACEAE (p. 52) . 



Division n. SPERMATOPHYTA. Flowering plants. 



Plants with true flowersi, reproducing by seeds, these containing an embryo. 

 Subdivision I. GTMNOSPEBMAE. 



Ovules not in a closed ovary. Trees with scalelike or needle-like evergi-een leaves, 

 the fruit a cone or berry. A single family PINACEAE (p. 60) . 



Subdivision n. ANGIOSPERMAE. 



Ovules in a closed ovary, this at maturity becoming the fruit. 



Class I. MONOCOTYLEDONEAE. 



Stems in cross section showing the vascular strands or fibers distributed irregularly 

 through the pith, as in the cornstalk; embryo with a single cotyledon; parts of the 

 flower usually in 3'8 or 6'8, never in 5'8; leaves usually parallel- veined. Our species, 

 with the exception of the genera Arundinaria and Smilax, are herbaceous. In some 

 groups the stems are hollow, except at the nodes; in these cases the vascular strands are 

 aggregate in the exterior zone and may appear as if in a ring. The leaves are net- 

 veined in Dioscorea, Trillium, and several other genera with broad blades, but even in 

 these they are ribbed with more or leas prominent main veins ruiming from base to 

 apex. In the family Lemnaceae there is no distinction between stem and leaf. In 

 some books this class is called endogens. 



Perianth none. 

 Plants free-floating aquatics, consisting of small ovoid or disk-shaped fronds, less 



than 10 mm. long LEMNACEAE (p. 114). 



Plants with stems and leaves, the latter sometimes reduced to scales. 

 Plants immersed aquatics, branching and leafy, the upper leaves often floating. 

 Flowers perfect, in spikes; leaves alternate. .POTAMOGETONACEAE (p. 62). 

 Flowers unisexual, axillary, the plants dioecious; leaves opposite. 



NAIADACEAE (p. 64). 



Plants terrestrial or growing in marshes, not immersed. 



Flowers subtended or surrounded by small bracts, and aggregate in spikelets; 



grasslike plants. (See also Sparganiaceae.) 



Leaves 2-ranked, the sheaths usually split; flowers with a second small bract 



(palea) next to therachilla; stems cylindric or flattened, usually hollow. 



POACEAE (p. 66), 

 Leaves 3-ranked, the sheaths not split; flowers with no second bract next 



to the rachilla; stems solid, usually triangular CYPERACEAE (p. 92). 



Flowers not subtended by bracts, unisexual, the staminate above, the pistillate 

 below on the same axis. 

 Leaves petioled, the blade (sometimes divided) net- veined; spike of flowers 



usually inclosed in a large spathe ARACEAE (p. 113) . 



Leaves not petioled, linear, elongate; spike of flowers not inclosed in a spathe. 



TYPHACEAE (p. 62). 



