290 POTAMOGETON ZIZII AS A BRITISH PLANT. 



petiole in large leaves reacliing an incli long, while the blade is 

 2-3^ inches long ; usually, however, the whole leaf, including the 

 petiole, does not exceed this length ; their form is narrow lanceo- 

 late-oblong, tapering at the base and acute or mucronate at the 

 apex ; the margin is really entire, but considerably undulated, and 

 so finely puckered as to appear irregularly crenate (exaggerated 

 in the plate) ; with a lens a few minute spinous denticulations 

 may be detected on the margin near the end of the leaf. The 

 lower leaves are considerably smaller (excei^t in a few luxuriant 

 and barren shoots), alternate, sessile or nearly so, with tai^ering 

 bases ; all are stiff, yellowish -olive green, and usually, especially 

 the lower alternate ones, strongly curved backwards. The stipules 

 are about l|-2 inches long, broad, acute and doubly keeled (not 

 winged) down the back. The peduncles are numerous, and rather 

 clustered at the top of the branches ; they are thicker than the 

 stems and become incrassated upwards, reaching nine inches or 

 even a foot in length, thus greatly exceeding the leaves ; the flower- 

 spike is about an inch long. I cannot detect any distinctive cha- 

 racters in the flowers ; the perianth leaves are broadly triangular 

 in outline with rounded angles, and very thick and concave ; the 

 fruit is smaller than that of P. liicens, but similar in form. 



It is thus clear that the plant chiefly differs from P. lucens in 

 its much smaller size, narrower and longer- stalked leaves with 

 entke margins, keeled instead of winged stipules, and more crowded 

 and prox)ortionately longer peduncles. In some of these points it 

 apiJroaches P. decipiens, which however has larger, more oblong 

 leaves, which are sessile and rounded at the base, and much shorter 

 peduncles. P. heteroplujUus is distinguished by its much smaller 

 and more numerous submerged leaves, which are scarcely crisped, 

 quite sessile, and narrowly oblong ; its stipules are not winged, 

 and when true floating leaves are produced they closely resemble 

 those of P. ohlouf/us. P. nitens, though its leaves (submersed) are 

 rather larger than those of P. heterophil I us, has them rounded and 

 semiamplexicaul ; the peduncles, too, in this species are much shorter. 



The difierent views with regard to the relationship of P. Zidi 

 wfll be best seen by tracing its history. The name was first pub- 

 lished in 1823 by Mertens and Koch," who state that they had 

 given it to a plant long familiar to them, in commemoration of the 

 discoverer, Dr. Ziz, and had used it in j\IS. tickets to friends, but 

 that they now only consider and call it var. latifolius of P. hetero- 

 phi/llus, Schreb. (P. (jraminem, Linn.) Koch continues to refer 

 it to that species in his more recent Flora,! and he is followed by 

 Kunth in his general monograph,]: and by Boreau.§ Apparently 

 the first author to publish ^' P. Zizii, 'Kooh.m.Miiy as a full 

 siDecies was Eoth in 1827 || ; and Eeichenbach^^ and Lange'^''^' also 



* in Kohling, ' DeutschJ. FJova,' i. ]>. ^45. 

 + Koch, ' Syn. Fl. Germ.' ed. 2, pp. 778 & 1028. 

 + Kunth, • Enum. Plant.' iii. p. 1:]1. 

 § Boreau, ' Fl. du Centre de France,' ed. 'i, ii. p. 000. 

 II Koth, ' Enum. Plant. Germ.' i. p. 031. 

 *\ Peich., ' Jc. Fl. Germ.' vii. p. '23. 

 ** hange, ' Haandb. d. Danske Fl.' ed. 3, ]). 133. 



