KTJNGL. SV. VET. AKADEMIENS HANDLINGAE. BAND 55. N:0 5. 



163 



netic position of P. linguatus, earlier a little doubtful (cf. Bennett in The Journ. 

 of Bot. 1902, 147!), can now be considered as fully settled by the knowledge of 

 the pistils. 



Distribution. South America, Chile austr., Llanquihue, 97, Dusen (hb. Stock- 

 holm.), Patagonia, Kark, 99, Borge (hb. Stockholm.), Tierra del Fuego, Betbederdal, 

 'Va 08, Skottsberg (hb. Uppsal). 



P. amplifoliiis Tuckerman. 



Observations on some New England Plants, in The American Journ. of Sci. 

 and Arts, 1848, 225-226. — Fig. 81. 



The submersed leaves are entire (without serrulation) and many-nerved; prin- 

 cipal nerves accompanied by lacunae; the last branching of the midrib takes place 

 above the middle as in P. hindostanicus and linguatus. 

 Ligules elongated and strong, with prominent sharp 

 double ridges at base. Styles a little thickened; stig- 

 mas narrow, with a long free part. Pollen spheric, of 

 middle-size. 



The floating leaves have the same form as in P. 

 natans, but differs from this and all the other species 

 by the very numerous (30 — 40) longitudinal nerves. The 

 stem-epidermis is provided with a one-celled strength- 

 ening layer typically lacking bast-bundles. Interlacunarly, 

 on the other hand, several circles of bundles occur in 

 the cortex. Endodermis of usual 0-cells; the arrangement 

 of the vascular bundles of the central stele prototypic. 



For the variations I refer to Ar. Bennett, Notes 

 on Potamogeton in The Journ. of Bot. 1904, 70. He 

 distinguishes three forms: var. ovalifolius Morong, f. 

 amphibius Benn. and an extreme form with larger submerged leaves than in general. 

 Of the first mentioned there are specimens in hb. Stockholm, from Manistee, Mich., 

 coll. by Morong himself and labelled »v. ovalifolius Morong » with his own hand. 

 I have also seen a form quite destitute of flaoting lecves, f. homophyllus, m. 



Distribution. N. America. Several specimens are present in the Swedish 

 Museums from Canada, Plevna, Ont. 02, Fowler (hb. Stockh.) and the United Sta- 

 tes gathered by Morong, Tuckerman (hb. Upps.) and Torrey (hb. Stockh.). How 

 far it extends to the north and the south is not fully explored. Small does not record 

 it in his Flora of the South-eastern United States, 1903. Robinson & Fernald in 

 Gray's New Manual, 1908, state, »N. Scotia to B. Columbia, south to N. Y., Ky., 

 Kan., and Col. » — Records from S. America, Argentina, no doubt refer to another 

 species, 



Fig. 81. P. amplifoUits Tuck. A. 

 Top of a snbmersed leaf, showing the 

 form and norvation (a little magnif.). 

 B, Pistil, sideview, y, st, stigma, sty, 

 style, oy, ovary. 



