160 



J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE rOTAMOGETONS. 



J 



VocdoM 



mm longis. Folia omnia petiolata larainis coriaceis ± tenuia; inferiora petiolis 

 longioribus laminis parvis, superiora petiolis brevioribus, ca. 75 mm longis, laminis 

 majoribiis, 65 — ^70 X 25 — 30 mm, ± 19-nerviis, oblongis, basi et apice rotundatis vel 

 apice siibcuspidatis; petioli ± biconvexi. Ligulce 30 — 50 mm longse subcaducse basi 

 obsolete bicarinatse. Spicse desunt. 



Anatomy of the stem : Epidermis-cells of usual form about 3 — 5 times as long 

 as the width; one-celled pseudo-hypoderma; no subepidermal strands. Cortex of 



usual structure with one circle of vascular and 

 bast bundles (about twelve in number). Endoder- 

 mis of 0-cells. The central cylinder presents an 

 vb eight-bundled diagram type. Bast-cells and other 



mechanical cells are few in number. 



Distribution. South Africa. Rhodesia, in 

 the Chimona River near the Lake Bangweolo in 

 stagnant water, Rob. E. Fries, 1911, n:o 691. 

 This is the only station from which this plant is 

 hitherto known. 



P. fibrosus n. sp, — Fig. 79. 



Caulis teres, 2 — 2,5 mm crassus. Folia supe- 

 riora oblonga vel ovato-lanceolata, brevissime et 

 obtuse cuspidata, 75 — 85 X 25 — 30 mm, 15 — 19- 

 nervia, nervo medio prominente, petiolata brunnea. 

 Ligulce inferne conspicue bicarinatse, ca. 40 mm 

 longse. Spica deflorata 45 mm longa, verticillis 

 quindecim. Pedunculus ut in P. natante. Fructus 

 non visus. Anatomia caulis: vide infra! 

 Only the three top most internodes of a spike-bearing shoot have been accessible, 

 in habit very much resembling a top of P. natans, or any other species with similar 

 floating leaves. It seems as if the leaf-base would hardly assume the subcordate 

 form characteristic to some other species. The styles and stigmas are overripe and 

 cannot, therefore, be described. Nevertheless the species can easily be distinguished 

 from all the other similar forms by the anatomic diagram of the stem. The epi- 

 dermis is provided with a one-celled strengthening layer and numerous bast bundles. 

 Interlacunarly there is one, and commonly a faint beginning to a second circle of 

 vascular- and bast bundles. Endodermis of 0-cells, central cylinder with 8 free vas- 

 cular bundles, each with strong bast elements along the endodermis and in the pith. 

 Those strong open bundle-sheaths are exceedingly significant of this species. 



The habitat of this plant is not surely known to me. The label bears only 

 a number, »91», but I am probably not mistaken, when supposing it to originate 

 from South Africa. 



The specimen here concerned is kept in hb. Stockholm. 



1 



vb 



Fig. 78. p. stagnofum Hao.stii. A, Trans- 

 verse section of the stem, ^^, cc, central cylinder, 

 /, lacunar system, vh, cortical bundles, e/>, epi- 

 dermis, lipy psendo-hypodernia. J3, Transverse 

 section of a petiole showing the five principal 

 vascular bundles {vh), the arrangement of the 

 lacunar system (/), the cortical bundles {ch) and 

 the subepidermal strands (sfr), ^-^. 



