212 J. O. HAGSTBÖM, CRITICAL RESKARCHES ON THE 1'OTAMOGETONS. 



with so narrow leaves, about 3—4 mm, may be an extremely rare thing. Among 

 many hundreds of specimens I at least never saw such a narrow-leaved Zizii-iorm. 

 The German auther G. Fischer regards P. Zizii as an indcpendent species chiefly, 

 as it seems, on account of the fruit-spikes of some forms, or (1914) at least some 

 forms from Switzerland, as a subspecies under P. gramineus L. and proposes to make 

 out the hybridity by ^Bastardierungsversuch zwischen P. lucens und gramineus* 

 (Bayer. Potamog. 1907). This way, however, is not performable, unfortunately. It 

 is much easier to examine the germinative ability of the seeds. I am persuaded 

 t hat P. Zizii very rarelv, if ever, propagates itself by seeds. And if even seeds able 

 to germinate were to be found, this fact, however, would not be an instance against 

 the hybrid origin, since hybrids now and then produce fertile seeds. P. Grakkner 

 in Potamogetonacese, 1907, and Synopsis, 1913, ranges P. Zizii as an independent 

 species at the side of P. lucens. The Finländer C. W. Fontell leaves the question 

 open (Beiträge Kenntn. anat. Potam., 1909, 63). 



All the specimens of P. Zizii I have had an opportunity to examine lack 

 independent, constant, specific characters and possess no othcr properties than those 

 found in P. gramineus and P. lucens, or which constitute a modification of the 

 characters of both, in perfect correspondence with the so-called intermediate characters 

 of the other hybrids of this genus. 



Thus it is characterized 1) by the mode of prolonging the stem (intermediate) 

 with often two (1 — 3) spike-bearing branches of the first and 2d (3d) rank; and by 

 the way, in which the branches below the primary spike branch again (often gramineus- 

 like). 2) Involucral leaves often subcoriaceous, most frequently with conspicuous 

 petioles, nearly without exceptions longer than the cusp. 3) Stem-leaves verv short- 

 })etioled (intermediate). 4) Branch-leaves al way s comparatively small if even the 

 stem-leaves are of lucens-eize. 5) The venation and strueture of the submersed leaves 

 obviously intermediate. 6) Ligules of an intermediate size and shape. 7) Fruit, if 

 present, also intermediate and most frequently infertile. 8) Stem-anatomv intermediate, 

 and so are also 9) the rhizomatic turios. 



As to habit P. Zizii appears in all conceivable transitions from the most gru- 

 mineus-like to the most ///rr». s-like forms. 



Its fruiting faculty appears, as it seems, in part of the crosses nearly quite 

 undiminished or normal, in most forms again considerably reduoed, and in many 

 cases, final ly, it is quite lacking, 



Very explanatory is the occurrence of /'. Zizii in Sweden. It is met with 

 locallv together with /'. gramineus and /'. lucens, spreading to the paralie] which is 

 the northern bonndary of /'. lucens hut not beyond, though /'. gramineus oontinues 

 to more northem latitudes. In other words, l\ Zizii lacks a distribution area of 

 its own, being dependent, for its spreading, on /'. gramineus and /'. lurens. Sweden 

 nia \ be the oountry of Europé vvhere /'. Zizii is most frequently mel with, bu1 

 there is no »independent species /'. Zizii» in Sweden. and as far as my experience 

 goes in no other contries either. 



As bo the stem-anatomj P. Zizii holds th(> medium between the two efficienl 



