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



longis ca. 170 — 225 mm. Ligulai olivaceas breviores et citius putrescentes quam in 

 P. natante. Spicce parvae steriles; pedunculi parum evoluti. 



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

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

 parent-species in anatomical respect as well as in the morphology. The author ex- 

 presses himself with some liesitation (»wahrscheinlich P. natans X polygonifolius») 

 which, however, is not heard of in his låter > Bemerkungen zu den Potamog. in d. 

 2. Aufl. der Synopsis d. mitteleur. Fl. von Asch. ii. Graebner, 1914». The above 

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

 It was gathered at Killarney, Ireland, by R. M. Barrington, in 1874 1 , and under the 

 name of P. natans 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. Aecording 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». Consequentry .Mr. Druce seems to have eome to the same conclusion 

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

 P. nata?is X any species of the Ghloéphylli (1. c., p. 458). 



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

 endodermis of ?7-eells, and reduced cortical strands [one subepid. circle, one com- 

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

 P. natans has more circles, P. polygonifolius only a subepidermal one, the Killarney 

 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 trichoides Cham. & Schl. (P. variifolius Thore, Essai d'une 

 Chloris du dép. des Ländes, 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. Rouy writes: >P. polygonifolius x gramineusl » (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 



1 The label runs thus: » Potamogeton polygonifolius var. linearis. Upper Lake Killarney. Kerry. R. M. 

 Bakkington 27 june 1874.» 



K. Sv. Vet. Akad. Hand). Band 55. N:o 5. 25 



