102 
bundles only. Subepidermal bast consisting likewise oi 
some small bundles. Endodermis-cells onesided thickened 
(= u-cells), like those of P. lucens. The central cylinder 
has one median and two lateral cavities or channels bet- 
ween which a wall of pith is situated. The median vascular 
bundle with two part of phloem formed by fusion of bundles. 
P. dentatus formes with P. lucens, gramineus, capensis 
illinoensis and ziziiformis a most natural group, all with 
lanceolate submersed leaves, lucens-nervature and -denti- 
culation, their central cylinder with reduced vascular 
bundles, u-endodermis and one to several circles of bundles 
in the cortex. Also P. vaginans, brasiliensis and Schwein- 
furthii might perhaps belong here. 
Our species likens much P. lucens f. acuminata but 
the fruit is different. It resembles also P. malaianus but 
with shorter petioles and more producted leaf-apices, the 
stem-structure moreover being another, etc. Hitherto only 
known from Japan, Yokohama. The examined plant is la- 
belled: »Japonia: Yokohama. ^ aug. 1862. Maximowicz. 
Iter secundum». Mus. petropol. 
Potamogeton orientalis n. sp. 
Caulis ramosus tenuis compressus (= P. obtusifolio 
et Hillii), internodiis brevibus, 5—35 mm longis, summo 
(spicæ proximo) interdum ad 40 mm; structura caulis cum 
ea P. Hillii conveniens ; folia caulina linearia, 50 mm longa 
2 mm lata, in apicem acutum æqualiter et sensim angustata, 
ad apicem 3-nervia, medio 5-nervia; costa mediana utroque 
striis albidis duabus instructa; nervi laterales principales 
in medio inter costam mediam et marginem siti, marginales 
sæpius tenuissimi, transversales pauci; folia ramorum mi- 
nora obsolete 3-nervia acuta subcuspidata; stipulæ deciduæ, 
10—15 mm longæ; pedunculi recti vel flexuosi, 15—25 mm 
longi; spica 10 mm longa 3— 4-verticillata subinterrupta; 
fructus et hybernacula desunt. 
P. orientalis has quite the same stem-structure as P. 
