187 



we take it to be the best to make it more independent and rank it separately in a 

 Suhsectio Nodosi: Gaulis teres simplex v. rarias ramosus. Folia natantia longepetiolata ; 

 submersa petiolata, media in parte et secundum nervös prsesertim principales valde 

 lacunosa, serrulata. Pistillum ut in AmplifoUis. Fructus magnus, laevis, carinatus. 

 Anatomia caulis: 0-endodermis, fasciculi corticales typice desunt; fasciculi tubi cen- 

 tralis liberi octo.» 



P. stag'norum Hagstr. n. sp. [Fig. 16]. — »Caulis ca, 30 cm altus, simplex, teres 

 vel subteres, internodiis inferioribus 50 — 75 mm longis. Folia omnia petiolata laminis 

 coriaceis + tenuia; inferiora petiolis longioribus laminis parvis + decurrentibus, superiora 

 petioils brevioribus, ca. 75 mm longis, laminis majoribus, 

 65 — 70x25 — 30 mm, + 19-nerviis, oblongis, basi et 

 apice rotundatis vel apice subcuspidatis; petioli + bicon- 

 vexi. Ligulse 30 — 50 mm longse, subcaducae, basi obsolete 

 bicarinatfB. (Spicae desunt.) 



Änatomy of the stem : Epidermis-cells of usual form, 

 about 3 — 5 times as long as wide. Strengthening layer 

 one-celled without Strands. Cortex of usual structure with 

 one circle of vascular and bast bundles (about 12 in 

 number) arranged as is shown in the adjoined figure. 

 Endodermis of typical 0-cells. Central cylinder with 2 me- 

 dian and 3 lateral bundles on each side, thus presenting 

 in all eight free vascular bundles, with eight separate 

 xylem cavities. Bast-cells and other mechanical cells few. 



Northeastern Ehodesia: in the Chimona river at 

 its mouth in the Lake Bangweolo, in stagnant water 

 [Sept. 20. — n. 691]. 



Affinity: Its nearest relatives are P. pulcher, F. Tep- 

 peri, P. Franchetii, P. Fryeri, P. Unguatus and P. am- 

 pUfoUus and a few species, not yet described, from S. 

 Africa, India, Australia aud America, at least 14 spe- 

 cies together, v/hich we rank in a Suhsectio AmpUfolii: 

 Caulis teres seepe simplex. Folia natantia longepetio- 

 lata, breviter-brevissime obtuseque mucronata, submersa + petiolata, saepe cuspidata, 

 ut plurimum cito putrescentia. Ligulse ssepissime caduca^. Stylus brevis superne 

 crassus vel incrassatus. Fructus magnus, Isevis, carinatus vel interdum ecarinatus. 

 Anatomia caulis: 0-endodermis; fasciculi corticales interdum adsunt, ssepius desunt; 

 fasciculi tubi centralis liberi, medii duo, saepe quatuor. » 



Fig. 16. Potamogeton stagnorum Hagstr. 

 — A. Querschnitt des Stammes, cc: 

 Zentralzylinder mit acht freien Gefäss- 

 bündeln; v: Rinde mit den grossen In- 

 terzellularen ; v: Gefässbündel in einem 

 Kreise in der Rinde geordnet, ^^/j. — B. 

 Querschnitt durch den Blattstiel, die 

 fünf in die Blattspreite eintretenden 

 Hauptgefässbündel, die Verteilung der 

 Interzellularen, die Gefässbündel der 

 Rinde (cb) und die subepidermalen Bün- 

 del (str) zeigend ; a: Oberseite, -^/j. 



