120 J. O. HAGSTHOM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



P. loClllOSUS n. sp. — Fig. 52. 



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

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

 cunosa (see fig. 52!). 



P. lacunfitiis n. sp. — Fig. 53. 



Caulis filiformis, subcompressus, ramosus ± elatus, internodiis 6- — -1 cm longis, 

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

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

 media in parte inter nervos laterales valde reticulosa, basi attenuata. Ligulce obtusee, 

 membranacese, caducse, biglandulosse, 6 — 7 mmlongse, paucinerviee. Pedunculus sequalis, 

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

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

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

 2 X 1,5 mm. 



Forma Novse-Anglife habitu graciliore foliis angustissimis, 0.5 — 0,75 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 over their whole width, at least always over the space between the lateral 

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

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

 nerves run near the margins, and grow 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 Novm-Anglice. It is pusiUus-\\ke, but a little 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 turios it behaves like P. 

 pusillus, ohtusifolius etc. It has numerous branches of the first, fewer of the second 

 rank, but elongates willingly dichotomously from the basis of the primary spike. 

 The turios consist of transformed branch-tops very near to those of P. pusillus and 

 foliosus, but a little weaker or slenderer. 



Both in the stem and the peduncle the vascular bundles fuse into a composite 

 one with common xylem channel. In the peduncle the subepidermal strands are 

 wanting. Stem and peduncle of rounded or suboval cross-cutform, central stele like- 

 wise. For the rest I refer to the fig. 53. 



