K0NGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. N:0 5. 193 



longis ca. 170 — 225 mm. Ligulce olivacese breviores et citius putrescentes quam in 

 P. natante. Spicce parvse steriles; pedanculi parum evoluti. 



Not having seen the Bavarian specimens I cannot pronounce an opinion on 

 them. They are said to appear as intermediate forms between tlie two suggested 

 parent-species in anatomical respect as well as in the morphologj^ The author ex- 

 presses himself with some hesitation (»wahrscheinlich P. nutans X q)olygonifolius») 

 which, however, is not heard of in his later sBemerkungen zu den Potamog. in d. 

 2. Aufl. der Synopsis d. mitteleiir. Fl. von Ascii. u. Graebner, 1914». The above 

 described form has proved to be a genuine hybrid of P. natans with P. polygonifolnis. 

 It was gathered at Killai'ney, Ireland, by R. M. Barrington, in 1874S and under the 

 name of P. 7iatans L. f. linearis, kindly sent to the writer by Mr Ar. Bennett, 

 who has also had the kindness of mentioning my view of the plant in The Journal 

 of Bot. 1908 p. 250. According to Graebner (Synopsis, 1912) this Killarney plant 

 is distributed as »P. natans X ■polygonifolius G. Cl. Druce, Rep. Bot. Exch. Club III, 

 1, 321, 1912». Consequently Mr. Druce seems to have come to the same conclusion 

 on the Killarney plant as the writer, whereas Graebner suggests a combination 

 P. natans X any species of the Chloephylli (1. c, p. 458). 



The stem anatomy exhibits a thin central axis with 8 free vascular bundles, 

 endodermis of [/-cells, and reduced cortical strands [one subepid. circle, one com- 

 plete and one incomplete (of 2 — 3 strands) interlacunar circle of vascular bundles]. 

 P. natans has more circles, /-'. polygonifolius only a subepiderzual one, the Killarnej' 

 plant keeps the medium. 



Probably it is the same plant of which Mr R. W. Scully writes in The Journ. 

 of Bot. 1889, 86: »in its most extreme form this plant (from Kerry) produces only 

 long capillary leaves and passes from this almost imperceptibly into P. natans with 

 floating leaves plicate at the base. Both Mr Bennett and Mr Fryer say that this 

 variety must be referred to P. natans instead of P. polygonifolius. » 



P. natans L. x triclioides Cham. & Schl. (P. Viariifoliiis Thore, Essai d'une 

 Chloris du dep. des Landes, 1803, 47). — Fig. 97. 



Ripe fruit was never, or extremely seldom, observed in this plant. Pollen is 

 also quite unfit for fertilization. That manifests the hybrid nature of the plant, 

 which is also confirmed by its solitary occurrence, in some rivulets of southeast 

 France, and by the variable anatomical stem-diagram. 



As evident as this fact is, just as difficult it seems to be to find out the two 

 species, a crossing product of which the plant must be. Nor has anyone hitherto 

 applied himself to this question in earnest. P. Graebner says, »planta dubia», and 

 includes it with his Javanici. G. Rouv writes: »P. polygonifolius X gramineusi ■" (Fl. 

 de France, T. XIII, 303). 



If we take the upper leaves as a starting point, it is quite clear that one of 

 the parent species must have been endowed with coriaceous leaves and further that 



' Tlie label runs thus: » Potamogeton polygonifolius var. Unearis. Upper Lake Killarney. Kerry. R. M. 

 Barrington 27 June 1874. » 



K. Sv. Vet. Akiui. Hnndl. BanJ 55. N:o 5. 25 



