152 



J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOQETONS. 



coriaceous-leaved species represent the prototype, since many species with floating 

 leaves, as we already have observed, have a reduced number of bundles and the 

 prototypic disposition also occurs in species with only submersed leaves. On investi- 

 gating in which species this prototypic arrangement appears, we shall find it mostly 

 in the coarser species, especially those with thick stems. From this fact the conclusion 

 may be drawn that the prototype may have been a coarse plant. As I have before 

 pointed out it has been provided with only submersed leaves, which have besides 

 been amplexicaul or sheathing, perhaps also serrulate like P. Rohhinsii and densus, 

 which obviously are ancient types. 



Beside the species treated of below we shall probably have to include P. montevi- 

 densis Ab. Benn., P. Delavayi Ar. Benn., and P. stenostachys K. Schum. with the 

 Amflijolii. The first mentioned has an endodermis of feeble ?6-cells bordering by it 

 upon the Colorati. Likewise P. parmatus Hagstr., of Madagascar, may perhaps be 

 referred to this group, or rather to the Co^orates-group, or it may be a combining 

 link between them. The position of P. Thunbergii is questionable. 



P. jamaicensis (Griseb.) cannot be a var. of P. plantagineus Dtjce. as is sup- 

 posed by the author of the Flora of the Brit. W. Ind. Islands, 1864, 506, but must, 

 according to the description, be referred to the Am-plifoUi as a proper species. 



On P. promontoricus m., see under the Colorati! 



P. pulclier TucKERMAN, Amer. Journ. of Science and Arts, 1843, 38. — Fig. 69. 



The stem of this species is 

 described as verrucose and black- 

 spotted (verrucosus: Tuck.; black- 

 spotted: RoBB., MoR.) yet without 

 a closer explication. These blackish 

 green papillse appear not only on 

 the stem but also on the peduncle 

 and petioles. They correspond the 

 coloured spots or papillse found in 

 many other species especially on 

 rhizomatic parts and at the base of 

 the stem, for instance in P. natans, 

 where thej' shade in a reddish-brown, 

 prcdongus, in which they have a 

 touch of yellow, and so on. They are organs or places arranged for secretions 

 especially dye-stuffs, and always situated at the thin cross-walls of the 

 outer channels. The dissolved pigment moves b}' degrees to the epider- 

 mis-cells and enter their outer walls which, therefore, are sometimes inten- 

 sively coloured. In P. pulclier the colour-warts appear in the shape of 

 small, usually oval or nearly circular, low swellings on the parts concerned. 



Fig. 69. P. puUlier Tuck. A, Trans- 

 verse section of a colour-wart and air- 

 lacana close by a septum, y. B, Radial 

 and longitudinal section through a colour- 

 wart, a, septum, ep, epidermis, hp, strength, 

 ening layer, y'. C, Pistil, side-view, ^^ 



