KUNGL. SV. VET. AKADEMIENS HANDLINGAE. BAND 55. N:0 5. 



129 



Beside the five species here treated of, four other, namely P. cristatus Reg. & 

 Maak, asiaticus Ak. Benn., numasalcianus Ar. Benn. and miduhikimo Mak. also be- 

 long to the Javanici. The group should be divided into, 

 three series: Suhjavanici (P. suhjav. m.), Eujavanici, and 

 Americani (P. Vaseyi Robb.). 



P. SUbjaVilllicilS n. sp. — Fig. 56. 



Caulis humilis ramosus vel simplex, subteres, filiformis, 

 internodiis brevibus (± 40 mm), ramulo brevi prolongatus. 

 Folia linearia attenuato-acuta trinervia, nervo medio utrin- 

 que stria albida instructo, nervis lateralibus versus marginem 

 sitis, caulina 60 mm longa, 1 mm lata, ramulina paulo bre- 

 viora et angustiora, natantia lingulato-lanceolata, in petiolum 

 decurrentia, 5-nervia, 25 X 2,5 mm. Ligulce membranacese 

 caducse, 7 — 10 mm longse, ima basi connatse. Pedunculus 

 brevis (12 mm) sequalis. Spica 3-verticillata. Appendices 

 staminorum longe unguiculati. Pistillum stylo conspicuo 

 stigmate anguste oblongo. Fructus non visus. 



Stem very slightly compressed, its epidermis with a one- 

 celled pseudo-hypoderma, endodermis of 0-cells as in all the 

 other Javanici, central cylinder of four vascular bundles fused 

 into one compound bundle with a common xylem air-channel. 

 Subepidermal strands consisting of 5 — 10 bast-cells. 



Midrib-part of the submersed leaf with faint or no 

 strands (in the fig. signed by a cross). For the rest the 

 submersed leaves present close resemblance to those of the 



,jep-hyp 



Fig. 56. P. snhjavanicus Hag- 

 STR. A, Two floating le.-ives of dif- 

 ferent form, \. B, Top of a sub- 

 mersed leaf, f . C, Transverse sec- 

 tion of submersed stem-leaf, mid- 



rib part; X occasionally occurring 



P. miduhikimo, but are almost more slowly tapering (seethe mechanical strands, 'r- a Trans 



*^ ■*■ ^ ^ verse section of stem, ep — ht/p^ 



fig.!). They are widest below the middle. The lateral nerves epidermis and pseudo-bypoderma, 



. . ,. . 1 -T T,,i 1 1 ,1 .. , 1 p. 1 s/d, strands, /, lacunae, 2 circles, 



join the midrib a little below the very tip as the fig. shows, cc, central steie, v. 



In shape and structure these leaves are also closely like the 



leaves of P. Preussii. The floating leaves of the material examined are narrow, but 



this fact may depend on special circumstances, and broader leaves might occasionally 



occur. They are widest at the middle or toward the top and by these leaves the 



species reminds very much of P. limosellifolius. 



The ligules are at least at the base connate and in the front-field 5 — 6-fibrous. 



We have referred P. subjavanicus to the Javanici chiefly on account of the 

 pistils coming very near to those of P. javanicus. But just as P. Preussii and P. li- 

 mosellifolitis form transition links to the Javanici, in the same way P. snhjavanicus 

 is, within the latter group, a transition form to the Pusilli. And if the fruit should 

 be found to correspond with that of the Pusilli, the species must be ranked there 

 in spite of the floating leaves. At all events it shows the close affinity between the 

 two groups. 



K. Sv. Vet. Altftd. Handl. Band 55. N:o 5. 17 



