152 



J. O. HAGSTROM, CBITICAL RESEARCHES ON THE POTAMOGETONS. 



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

 leav r es, as \ve 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, \ve shall find it mostly 

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

 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. Bobbiiisii and densus, 

 which obviously are ancient types. 



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

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

 Amplifolii. The firat mentioned has an endodermis of feeble «-cells bordering by it 

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

 referred to this group, or rather to the Coloralus-group, or it may be a combining 

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



P. jamaicensis (Griseb.) cannot be a var. of P. plantagineus Ducr. 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 Amplifolii as a proper species. 



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



P. puldicr Tuckerman, Amer. Journ. of Science and Arts, 1843, 38. — Fig. 69. 



i,,. The stem of this species is 



dcscribed 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 spöts or papillse found in 

 many other species especially on 

 rhizomatic parts and at the base of 

 the stem, tor instance in /'. valans. 

 where they Bhade in a reddish-brown, 

 prcelongws, in which they have a 

 touch o!' yellow, and so on. They are organs or places arranged for srcrctions 

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

 outer channels. The dissolved pigment moves by degreea to the epider- 

 niis-cclls and enter their onler walls which, therefore, are sometimes inten- 

 sively coloured. In /'. piih/nr the colour-wart s appear in the shape ol 

 small, iisuallv oval or aearly circular, lo w swellings on the parts oonoerned. 



Fig. 69. /'. puleher Tuck. I. Trans- 

 verse seotion n! b oolour-waH and air- 

 lacona close bj a septnm, ,'. '•'• Bidial 



and longitndinal Becl tbrongh ■> colonr- 



wnrt, a, septam, ep, i pidermis, hp. Btrengtb. 

 ening laj er, , '■ ' '■ Pistil, Bide-^ n» . ' } 



