78 J. O. HAGSTRÖM, CR1TICAL RESEARCHES ON THE POTAMOGETONS. 



might be one of the parents beside P. zosterif., I låter on, after further minute exa- 

 mination, have got still more convinced of the accuracy of the above presumption. 



Stem more or less flattened but not winged, crosscut-form oval, the longer 

 axis about twice the shorter one. Central cylinder with one cavity, round which 

 the phloem parts are grouped as in P. trichoidcs. Leaves narrowly linear, stem- 

 leaves 1,5— 1, tö mm, with somewhat broad base, sometimes long with trichoidcs-Yike 

 apex, sometimes shorter with an apex more like P. zosterifolius. Stem-leaves 5-nerv- 

 ed and with strong bast-bundles in the lacunar part. Air-channels arranged as in 

 P. trichoidcs. Turios as to shape and other conditions intermediate, inner leaves 

 sometimes confined within the sheaths, sometimes a little protruding. The lower 

 leaves resemble most those of P. trickoidas. Peduncles elongate, 3 — 5 cm long, their 

 anatomical structure intermediate: the two middle bundles in proximity to each other 

 as in P. trichoidcs. Spike of four verticils, always barren. A single nearly ripe 

 fruit, once found, looked very much like a trichoides-iruit. About 50 p. C. of the pol- 

 len is sterile, the rest consisting of bigger (F. zosterif.) or smaller (/\ trick.) grains. 



Two forms may be distinguished: 



i', apicataa n. f. — Folia elongata, (10)— 12— 15 cm, in apicem acutissimum 

 sensim attenuata. 



f. breviusctilus n. f. — Folia 6— 8 — (10) cm longa apice citius attenuata. 



By the long leaves the former reminds of P. zosterifolius, the leaves never- 

 theless being narrower and the top unlike, the latter, again, of P. trichoidcs but 

 has much broader leaves. 



Distribution. Denmark, Varmingsö, 97, Baagöé (hb. Stockholm.), /. apicalus; 

 Nibså, 00, Baagöe (hb. Stockholm.), /. breviusculus. Both forms probably originate 

 from the same crossing. More habitats are not yet known. 



Subsectio 9. Ochreati Graebner. 



Graebner, Potamog. in A. Engler, Das Pflanzenr. 1907, 100. 



Caulis compressus internodiis ± elongatis, nodis annulatis. Folia multinervia 

 obtusa vel mucronulata, basi rotundata, canalibus in medio perpaucis. Ligulso fissaB, 

 multinerviae. Pistillum stylo conspicuo sequali, stigmate parvo. Fruclus tricarinatus, 

 sa^pe rugosus. 



This and the two following groups nearly associate with Coinprcssi by the 

 broad, rounded leaf-base and the richly developed sclerenohyma of the Leaves and 

 ligules, hut differ by the style and stigma, that one more clongated, this one smaller 

 and more rounded. The group is evidently nearest relalcd to the Potygoni, also with 

 elongated styles, though a liltlc thiokened upwards, and with a very rich laounar 

 system in the leaves. The present group also separates from all the following bhrough 

 the l— 3-celled hypodermatous layer in the stem anatomy. In this respeot it seems 

 to take the lirst plaoe of all the aarrow-leaved groups. — Sibernating buds are not 

 known either in this group or in th<' two following ones. 



