186 



exhibits two median va.sc. bundles with common xylem cavity and oue Compound lateral 

 bündle on each side. Bast-cells placed on both sides of the median bundles as the 

 tiijure shows. 



The rhizome differs anatomically in the liypodermatic Stratum beino- 2-celled without 

 bast-cells bat with scattered thick-walled mechanic cells and by a stouter central stele 

 with 8 free bundles and two median cavities. Cortex with three circles of lacuna? of 

 about the same size. 



The structure ot" the leaves is that common to the submersed leaA'es in general. 

 No mechanic cells are observed in the lacunar part round the principal vascular bündle. 

 A faint marginal strand as usual. Besides we refer to the figure. 



Northeastern ßhodesia: Lake Bangvveolo near Kasomo [Sept. 19. — n. 655]. 



Though without spikes and fruit this species is easily recognizable through the 

 characteristics mentioned above and cannot be confounded with any species known 

 to nie. It is not clear whether P. repens can produce curiaceous Hoating leaves 

 or not. 



ÄJf'mitij. Undoubtedly the species is related to some Australian and South 

 American species which must be established as a separate group, Suhsectio Sderocarpi: 

 Gaulis teres simplex vel subsimplex. Folia natantia parva, apice rotundata aut nulla; 

 submersa obtusa, brevipetiolata vel sessilia, vaginse caducse. Pistillum stylo brevi 

 incrassato aut fere nuUo. Fructus minor v. media magnitudine, tricarinatus. Anato- 

 mia caulis: fasciculi vasculares tubi centralis duo, in medio sejuncti, laterales etiam dno 

 rarius plures. 



The bulk of this group belongs to Australia and New Zealand (F. Clieesemann). 

 But it is verv interesting to see how the P. sderocarpus of Brazil and P. repens of 

 Rhodesia connect the Floras of Africa and South America with that of Australia. 

 No Indian species of this subsection are known. The same is the case with another 

 nearly related Australian group to which belong P. sidcafMS, P. tricarinatus and othevs, 

 not yet described, and w^hich is represented by one species, though not yet described, 

 in South America, but nowhere eise». 



P. nodosus Poir. (Sj^n. P. fluitans auct.) var. Billotii (F. Schultz) f. angustissimus 

 Hag-str. n. f. — »Folia submersa longe producta ane^ustissima. » 



Khodesia: in dem Sambesi-Fluss, oberhalb der Victoria Falls [n. 187]. 



Diese beinahe kosmopolitische Art wird von Bennett (in Fl. trop. Afr. 8, S. 219) 

 für Angola und Nord- und Südafrika angegeben. 



»This species, although with most of its properties corresponding with the Amplifolius- 

 group, occupies by its one-celled leaf-teeth (see Hagsteöm in Bot. Notiser, 1908, p. 100) 

 an intermediate position between the group just mentioned and the Lucentes Grraebn., and 



