564 NAIAD ACE.E. (PONDWEED FAMILY.) 



26. P. TllCkermani, Robbins. Very slender and delicate from a creeping 

 rootstock, of a fine light green ; stem filiform with several short and repeatedly 

 dichotomous leaf-bearing branches ; leaves thin and flat, but setaceous and ta- 

 pering to near the fineness of a hair (1-4' long and |" extreme width), obscurely 

 1 - 3-nerved, with a few coarse reticulations ; stipules rather persistent below, 

 J' long, obtuse ; peduncle solitary, very long, rather thickened upward ; spike 4 - 

 S-flowered f in fruit continuous, oblong ; fruit thick-lenticular, obscurely 3-keeled ; 

 nutlet slightly impressed on the sides ; shell thick and hard ; embryo nearly an- 

 nular. Cold ponds, White Mountains of N. H., N. Y., and N. J. 



# # Stipules united with the sheathing base of the leaf. 



27. P. peetinatus, L. Stem filiform, repeatedly dichotomous ; leaves very 

 narrowly linear, attenuate to the apex, 1 -nerved with a few transverse veins; 

 spikes interrupted, on long filiform peduncles ; fruit obliquely broad-obovate, 

 compressed, bluntly keeled ; shell of nutlet very thick ; embryo spirally incurved. 

 N. Brunswick to Fla., westward across the continent. Aug. -Oct. (Eu.) 



28. P. marinus, L. Resembling narrow-leaved forms of the last species, 

 low and very leafy ; peduncles much elongated ; fruit much smaller (l"long) 

 and thinner, round-obovate, not keeled upon the rounded back, tipped with the 

 broad sessile stigma; embryo annular. Western N. Y., 111., Mich., and south- 

 ward. Probably the range of this species is much more extensive than indi- 

 cated, as it has been confounded with P. pectinatus. 



29. P. Robbinsii, Oakes. Stem ascending from a creeping base, rigid, 

 very branching, invested by the bases of the leaves and stipules ; leaves crowded 

 in two ranks, recurved-spreading , narrow-lanceolate or linear (3 - 5' long and 2 - 

 3" wide), acuminate, ciliate-serrulate with translucent teeth, many-nerved; stip- 

 ules obtuse when young, their nerves soon becoming bristles ; spikes numer- 

 ous, loosely few-flowered, on short peduncles; fruit oblong-obovate (2" long), 

 keeled with a broadish wing, acutely beaked ; embryo stout, ovally annular. 

 In ponds and slow streams, N. Brunswick to N. J., the N. shore of L. Superior, 

 and far westward. 



4. B IIP PI A, L. DITCH-GRASS. 



Flowers perfect, 2 or more approximated on a slender spadix, which is at 

 first enclosed in the sheathing spathe-like base of a leaf, entirely destitute of 

 floral envelopes, consisting of 2 sessile stamens, each with 2 large and separate 

 anther-cells, and 4 small sessile ovaries, with solitary campylotropous suspended 

 ovules ; stigma sessile, depressed. Fruit small obliquely ovate pointed drupes, 

 each raised on a slender stalk which appears after flowering ; the spadix itself 

 also then raised on an elongated thread-form peduncle. Embryo ovoid, with a 

 short and pointed plumule from the upper end, by the side of the short cotyle- 

 don. Marine herbs, growing under water, with long and thread-like forking 

 stems, and slender almost capillary alternate leaves, sheathing at the base. 

 Flowers rising to the surface at the time of expansion. (Dedicated to H. B. 

 Ruppius, a German botanical author of the early part of the 18th century.) 



1. R. maritima, L. Leaves linear-capillary ; nut ovate, obliquely erect, 

 1-J-" long; fruiting peduncles capillary (3-6' long); stipes 1-12" long. 

 Shallow bays, along the entire coast ; also occasionally in saline places in the 

 interior. (Eu., Asia, etc.) 



