120 J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETON9. 



P. locilloSUS n. sp. — Fig. 52. 



P. habitu P. obtusifolii M. & K. Caulis subteres ramosus. Folia linearia ob- 

 tusa mucrone minutissimo trinervia, ad nervum medium valde usque ad apieem la- 

 c u nosa (see fig. 52!). 



P. lacunatus n. sp. — Fig. 53. 



Caulis filiformis, subcompressus, ramosus ± elatus, internodiis 6 — 7 cm longis, 

 superne brevioribus, supra spicam primariam dichotome prolongatus. Folia linearia. 

 trinervia, subcuspidata — subacuta, caulina 4 — 6 cm longa, 1 — 1,5 mm lata (0,5—0,75), 

 media in parte inter nervös laterales valde reticulosa, basi attenuata. Ligula; obtnsse, 

 membranacese, caducae, biglandulosae, 6 — 7 mm longa?, paucinervise. Pedunculus sequalis, 

 brevis, 10 — 20 mm longus. Spica minima, capitata, biflora. Folia perianthii rotun- 

 data, breviter unguiculata. Pollen globosum, parvum. Pistill um stylo brevissi, mostig- 

 mate rotundato. Fruetus rotundatus, siccus subcarinatus, lateribus subcompressus, 

 2 X 1,5 mm. 



Forma Nov»-Angliffl habitu graciliore foliis angustissimis, 0.5 — 0,:r> mm latis. 



As to habit and form and size of the leaves this species is extremely like P. 

 pusillus. A closer examination of the leaves, however, shows the difference at once. 

 Nearly över their whole width, at least always över the space between the lateral 

 nerves, they are endowed with small channels. By this the present species among 

 all species within the pusillus-group comes nearest to P. confervoides. The lateral 

 nerves run near the margins, and grovv very faint towards the top of the leaf, where 

 their course can only be traced by greater enlargement. They join the midvein as 

 is shown in the fig. In the lacunar part mechanical strands are usually wanting 

 or occur occasionally, but very sparingly. The leaves get their firmness from the nu- 

 merous longitudinal and transverse walls of the lacunae. Fruit is observed only in 

 the form Novce-Anglice. It is pusillus-Yike, but a littlc broader above, 1.5 mm. The 

 spikes are only biflowered, capitate; pistils four in number. 



Pollen is well developed and abundant so that the plant can not be suspected 

 to be of hybrid origin. 



As to the ramification and in the development of fcurios it behaves like /'. 

 pusillus, obtusifolius etc. It haa numerous branchea of the first, fewer of the second 

 rank, bul elongates willingly dichotomously from the basis of llu- primary spike. 

 The imios consist of transformed branch-tops verv near to those of /'. pusillus and 

 foliosus, but a little weaker or slenderer. 



Both in the slctn and the pedunele the vascular bnndlea Inse into a oomposite 

 one with common xylem channel. in the pedunele the subepidermal stranda are 

 vranting. Stem and pedunele of rounded or Buboval cross-cutform, central Btele like- 

 wise. Por the rest I refer to the fig. 5!{. 



