KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. NIO 5- 



153 



The epidermis, otherwise in general consisting of elongated cells, about 5 times 

 as long as broad, consists here of very short cells of more or less regnlar cubic 

 form. Inside the epidermis settle 2 — 4 layers of parenchymatous cells of the 

 same form as the common cortical cells, but to the size generally a little smaller 

 than those. The bottom of the lacuna is extended across those cells (Fig. G9, B, a). 

 In species with 2- or more-celled pseudo-hypoderma no increase takes place and, there- 

 fore, no external protuberances are to be found. P. pulcher has only a single cell- 

 stratum and, accordingly, papillse are formed. 



As the figure above shows P. pulcher has only a single strengthening stratum 

 and lacks subepidermal strands. Interlacunar strands occur neither in the stem nor 

 in the petioles. The central stele of the stem is surrounded by an O-endodermis. 

 Vascular bundles arranged according to the diagram in fig. 80 with four median 

 bundles, thafc is to say a bundle-trio and an opposite bundle. 



The species can easily be recognized by its narrowly ovate-lanceolate, short- 

 petioled, submersed leaves with broad lacunar part along the midrib as far as the 

 very apex and feeble ligules. The pistils are those typical to the group. Pollen 

 small-grained. 



The species occurs also without true submersed leaves: 



f. smphibius n. f. — Fol. omnibus coriaceis vel subcoriaceis. 



Distribution: U. S. of N. America: Delaware, 74, Canby (hb. Uppsal.), Nov. 

 Angl., Tuckerman (hb. Uppsal.), Massachusetts, severa] stations: Ashland, Naticks, 

 Readvill, 80—82 — 83, Morong (hb. Stockholm.), f. amphibius; Apponang Pond, Rhode 

 Island (hb. Stockholm.). 



P. rot uml atus n. sp. 



Fig. 70. 



Caulis subhumilis (± 30 cm) teres simplex, internodiis 2 — 5 

 cm longis, a foliis floralibus ramis l:se — 2:se ordinis prolongatus. 

 Folia submersa subcoriacea, infimum phyllodio simile, cetera longe 

 petiolata lanceolata obtusa; natantia coriacea longe petiolata 

 oblonga v. oblongo-lanceolata subcuspidata, 50 — 75 X 20 — 30 mm, 

 13 — 19-nervia, subprasina. Ligulce membranacese ecostatae badire 

 caducae cito pntrescentes. Pedunculus aequalis, 5 — 8 cm longus. 

 Spica florens 22 — 25 mm, fructificans 25 — 35 mm longa. Pollen 

 globosum. Pistillum stylo brevi, stigmate parvo ovali-suboblongo. 

 Fruetus oblique obovatus brevissime rostratus, dorso rotundatus 

 ecarinatus, latere ventrali saepe inferne sinuatus, 3 X 2,25 mm. 



The colour of the floating leaves of this species is usually 

 prasinous, the shape oblong-lanceolate, their petioles of equal length 

 to the blade or longer. The lower leaves are subcoriaceous, but 

 with longer petioles and narrower lamina. Ligules membranous 

 and without ridges. Peduncle of the same thickness as the inter- 

 node next below or a little thicker. 



K. Sv. Vet Akad. Handl. Band 55. N:o 5 



Fruit of middle-size thorough- 



Fig. 70. P. rotundatus 

 Hagstii. A, Floating leaf J. 

 B, Pistil, side-view, niagni- 

 fied. C, Fruit, side-view, !. 



20 



