KUNGL. SV. VET. AKADEMIENS HANDLINGAR, BAND 55. N:0 5. 169 



Distribution. South America, Lagunas de Pictina, Cordoba, La Plata, 77, 

 HiERONYMUS (hb. Stockholm.)- 



Subsectio 19. Sclerocarpi Hagste. 



Caulis teres simplex v. subsimplex. Folia natantia parva apice rotundata aiit 

 nulla; submersa breviter petiolata v. sessilia obtusa; ligulje caducaj. Pistillum stylo 

 brevi incrassato aut fere nuUo. Frucius minor v. media magnitudine tricarinatus. 

 Anatomia caulis: fasciculi vasculares tubi centralis duo in medio sejuncti, laterales 

 etiam duo rarius plures. Endoderniis, vide infra! 



The styles of the species I here class together are not yet fully known. This is 

 true about P. Drummondii, P. porrigens m. and P. repens m. In the South American 

 P. sclerocarpus the style is very short and thin, in P. reduncus m. extremely insignificant, 

 but in P. Cheesemanii more conspicuous and incrassate, by which this species draws 

 near to the next group. The Australian species, however, seem to be more in accordance 

 with the South American, Indian, and African species than with the European. 



Anatomy of stem: Typically we have here no pseudo-hypoderma (exception: 

 P. repens m.) but often subepidermal mechanical strands; no cortical bundles are 

 observed. Endodermis of 0- cells often with a faint tendency of forming feeble u- 

 cells at intervals. By this character the group approaches to the subsequent group, 

 but differs from it by the particular central axis, which exhibits two median and 

 two lateral xylem canals, one on either side, separated by mechanical tissue. The 

 type is accordingly four-bundled. The median cavities seldom unite into a common one 

 as sometimes in P. repens m. Concerning the anatomic deviation of the Hokianga- 

 plant (see under P. Cheesemanii!), which presents more lateral bundles in the cen- 

 tral stele than the type, this is accounted for by the fact, that in shallow-water-forms 

 in general, as also in the basal parts of high-grown species with reduced lateral 

 bundles, this reduction or fusion does not at all or but partly take place. 



Like the preceding this group is also chiefly an Australian one, and P. ausiraliensis 

 Ar. Benn. might belong hereto (or to the Muricati?) rather than to the Colorati. 

 The description of P. Drummondii seems to involve two different species. The genuine 

 P. Drumm. is to my opinion long-peduncled and richly provided with floating leaves 

 of about the size 30 X 13 mm. 



P. scleroctarpus K. Schum. 



Flora Brasiliensis, III, 3, 1894, 688, t. 120. — Fig. 86. 



The specimen of »Minas Geraes, Congo secco» I have examined has very short 

 internodes (4—8 mm) at the lower half of the stem, higher up a little longer, 10 — 

 50 mm, and the stem is prolonged by 1 or 2 branches from the primary spike, 

 otherwise unbranched. Floating leaves long-petioled with small laminae of oblong 

 lanceolate form and obtuse, 30 x 10 mm, 13-nerved. Submersed leaves linear-lanceo- 



K. Sv. Yet. Ak.icl. Ilaiidl. Band ,55. K:o 5. 22 



