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



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

 pect.!) 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. pectinaius. 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 Sodbrlxjnd, 1886 (hb. Lund.). 



6. f. alandicus n. f. — Statura humili, internodiis brevissimis; prseterea ut 

 in prsecedente. 



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



7. f. Wahlenlbergii n. f. — Gaulis 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. filif ormi; 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 over vast regions. In P. filiformis 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 Wahlenbergii is a 

 very 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, Wahlenbbrg (hb. Stockholm., 

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



S. 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. Kerner v. Marilaun at 

 Giessen, Innsbruck, in the year 1866; later also found in cold rivulets at Egerdach 

 (common) and Seefeld (Innsbruck). 



In his herbarium Kerner has labelled the plant P. juncifolius remarking 

 that the fruit by its slight size and low beak associates the plant with P. marinus 

 L. {= filif. Pers.) and that in habit it is like P. zosteraceus Fr. D:r G. Tiselius 

 (in Bot. Not. 1884, 91 — 92) and Ar. Bennet (in Flora exsicc. Austro-Hung.) held 

 it at first to be P. flabellatus Bab. Tiselius has later on defined it to be a distinct 

 species. He observes, that the fruits are few in number and closely resembling 

 those of P. vaginatus, that the leaves are of equal width up to the obtuse apex etc. 



