HTDROPTERIDES. (mARSILIACE^.) 677 



velum, the free part spotted; macro^pores yery yariable in *ize {0".22-0".3O 

 wide), the upper segments covered by short crested ridges, which on the Jower 

 hemisphere run together forming a network ; microspores larger than in any 

 other species except No. 1 (0".013-0".016 long), mostly somewhat tubercu- 

 lated. — Gravelly banks of the Delaware, from above Philadelphia to Wil- 

 mington, between flood and ebb tide; margins of ponds, New England {Roblins, 

 &c.), and northward. — Distinguished from the nearly allied I. lacustris by the 

 stomata of the leaves, the spotted sporocarp, the smaller si?e of the spores and 

 their reticulation on the lower half. 



6. I. Engelmtoni, Braun. Leaves long (25-100, 9'-20' long), light 

 green, erect or at last prostrate, flat on the upper side ; sporocarps mostly ob- 

 long, unspotted, the velum very narrow; macrospores (0".J9-0".24 wide) cov- 

 ered all over with a coarse honey-comb-like network; microspores {0".012- 

 0".014 long) mostly smooth. — Shallow ponds and ditches, from Massachusetts 

 (near Boston, W. Boott, H. Mann) to Pennsylvania and Delaware and (prob- 

 ably through the Middle States) to Missouri. —By far the largest of our species, 

 often mature in July. 



Var. gracilis. Leaves few (8-12 only, 9' -12' long) and very slender; 

 both kinds of spores nearly as in the species. — Southern New England, ap- 

 parently in deep water. 



Var. v^lida. Trunk large and stout (often l'-2' wide); leaves (50-100, 

 even 200, 18'- 25' long) with an elevated ridge on the upper side; sporocarps 

 oblong or linear-oblong (4"- 9" long), one third or one half or more covered by 

 the velum; both kinds of spores very small, macrospores 0".16-0".22 wide, 

 microspores 0".011 -0".013 long, spinulose. — Delaware ( >r. M. Canby), and 

 Pennsylvania {Prof. Porter). Sept. 



7. I. melau6poda, J. Gay. Leaves (15-50, 6'- 10' long) very slender, 

 keeled on the back, straight, bright green, usually with dark brown or black 

 shining bases ; sporocarps mostly oblong, with a very narrow velum, brown or 

 spotted; macrospores very small (0".14-0".18 wide), smoothish, or with faint 

 tubercles or ridges; microspores (0".010-0".012 long) spinulose. — Shallow 

 ponds, and wet prairies and fields. Central and Northern IlUnois (E. Hall, 

 Vasey), and westward. June, and sometimes again in November. — Trunk 

 more spherical and more deeply 2-lobed, and both kind of spores smaller than 

 in any other of our species ; leaves disappearing during the summer heat. 

 Closely approaching the completely terrestrial species of the Mediterranean 

 region. 



Two other species, J. rf.4-GGiBA, Sbuttleworfh, and I- ChapmIni, Engelm., 

 arc found in Florida ; and three piore, I. Nuttallii, Braiajj, I, Califoknica, 

 Engelm., and I. pygm^a, Engelm., in the Pacific States. 



Order 132. HYDBOPTEBIDES. (Marsiliace^, K. Br.) 



Aquatic cryptogamous plants, of diverse habit, with the fructijlcation borne 

 on submerged branches, consisting of two sorts of organs, contained in irreg- 

 ularly bursting involucres (sporocarps): — here represented by only two 

 genera. 



