22 J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



This form is much like the P. pectinatus var. ungulatus Hagstr. (see under P. 

 pect.f) as to the leaf-apex. However, the half of the pollen-grains are deformed and 

 the well-shaped grains smaller and of another form than in P. pectinatus. In this 

 species the grains are always more or less conspicuously oblong, in the present form 

 they are almost completely spheric. The diminution of the grains (influenced by 

 P. filif.) has been made at the expence of the length. — 



Habitat: Sweden, Blekinge, Ysane, coll. by Söderlund, 1886 (hb. Lund.). 



6. f. alamlicus n. f. — Staturå humili, internodiis brevissimis; praeterea ut 

 in praecedente. 



Habitat, Finland, Alandia, Saggö, 97, Sernander & Olsson (hb. Uppsal.). 



7. f. Wahlénbergii n. f. — Caulis elongatus habitu P. pectinati. Folia fusco- 

 viridia 100 X 0,75—1 mm vaginis badeo-marginatis ± 20 mm longis, junioribus in- 

 tegris (P. filif.). Pedunculus 4—5 cm; spica 3 — 4-verticillata verticillis approximatis, 

 parviflora; stylus ut in P. filiformi; sterilis. 



The apex of the leaves is abruptly formed to a short, sometimes only ver- 

 rucose, subobtuse point. From the upper leaf-axils (more exactly expressed, from 

 the basal scales of the primary upper branches) there often grow out rhizomatic 

 shoots just as in P. pectinatus, though of slender structure, an occurrence often met 

 with in other forms of this hybrid for instance in f. Hartmanii and f. Kerneri, see 

 below. Through those rhizomes and their turios the plant, though sterile, has an 

 excellent mode of spreading över väst regions. In P. filiformi s we have scarcely ob- 

 served such rhizomes in the leaf-region. 



As to the stem-structure it may be remarked that also in this form 2 — 3 

 strands occur in the cortex at the middle of the stem. Forma Wahlénbergii is a 

 verv instructive form since the two parent-species most evidently appear in it and 

 both, so to say, contest one with the other to put forth their peculiarities. 



Distribution. Sweden, Uppland, Fyris at Ulfva, Wahlenberg (hb. Stockholm.. 

 Uppsal.). A similar form is coll. in Norway, Jsederen 75, Bryhn (hb. Christian.). 



ö. 



Obtusus Hagstr. 



8. f. Kerneri n. nom. P. juncifolius Kerner ap. Fritsch in Verhandl. 

 K. K. Zool.-bot. Gesellsch. in Wien, Wien 1896, 364—366. Fig. 5. 



This form is for the first time gathered by Prof. A. Kernkr v. Marilaun at 

 Giessen, Innsbruck, in the year 1866; låter also found in cold rivulets at Egerdaoh 

 (common) and Seefeld (Innsbruck). 



In liis herbarium Kerner has labelled the plant P. juncifolius romarking 

 I liat the fruit by its slight size and low beak associates the plant with P. marinits 

 L. ( filif. PERS.) and that in habit it is like P. zosteraccus Fr. D:r G. Tiselius 

 (in Bot. Not. 1884, 91 — 92) and Ar. Be NN ET (in Flora oxsicc. Austro-Hung.) held 

 it at first to bo l*. flabellatus Bah. Tiselius has låter on defined it to be a distinot 

 species. He obscrvos, that tlio fruita are few in number and closely resembling 

 those of /'. vaginatus, that the leaves are of equal width uj) to the obtusc apex etc. 



